I know someone is going to get mad because I gave my opinion....
For starters, you asked this is in the M8 forum. Of course, they who are happy with it will tell you they think it is better than the icon

Just like if you asked in the Icon forum, you'd get the same response. So it will be hard pressed to get impartial responses.
Let me get my bias aside....I use Lumia and only Lumia windows phone. I am slightly considering getting the HTC one m8 for att as I really want a new phone. I've been rocking a Lumia 1520 for nearly a year now and I've grown bored with it. That being said, it is the best windows phone out to date(the icon being a close second) so i'd never replace it with an M8 as my primary phone. I'll probably wind up with a Lumia 830

That still is a better phone for me plus it has features the M8 won't have, like Hey cortana.
It's a shame that you can't get the 1520 but you do have the Icon and the Icon is merely a 1520 in a smaller package without glance or a SD card slot. Glance is cool and all but ehh. And the SD card slot is only necessary because the att version of the 1520 has 16 GB storage.
Back to your situation
The M8 is a great phone and beautiful hardware. However to me, the phone itself seems to be a phone that does some things cool but it is not a Jack of all trades phone. Its camera sucks compared to most lumia but it is faster(See what I mean). It does have those great speakers but then again those speakers actually make the phone look less attractive to me. Just my opinion.
I believe the Icon is a Jack of all trades phone. It is a full package phone. Great hardware, Great camera(Actually Superb camera) and Great microphones and wonderful screen technology and of course it's a Lumia so it does have Lumia centric apps and if Microsoft/Verizon manages to work out the updates...which I have faith Microsoft is going to do their best, Cyan and Denim add things that the M8 doesn't have and we are unsure we're getting.
The M8 will solve your Windows Phone 8.1 yes problem but not Cyan since that is Lumia centric.
Personally, you asked if I think a phone is coming out in 6-8 months? Probably so. That's when Windows 10 comes out and I can't really see Microsoft NOT having something being announced. Their last flagship in America was announced in February.
If something doesn't come out within the next 6-8 months, I'd be highly upset simply because that means this OS will be way behind. No flagship in over a year. I don't consider the M8 a flagship...it is a flagship but it is not the Hero device of the Windows Phone line. That's what Lumia is for, imo, hence why most people are inquiring about updated 1020 and 1520 models as THOSE are the type of phones most people want.
For those who say that the Lumia Icon NEEDS cyan....it doesn't need Cyan. It certainly makes the phone better but there are plenty of Icon owners who are happy with their Icons on Windows Phone. They simply want the latest update(which isn't actually the latest now that denim is out) and that is understandable.
My boyfriend has an Icon, which is such a lovely phone, and is happy with it and he can't really see much difference in his Icon over my 1520. He is fine on Windows Phone 8 and enjoys it as such and he is about to try to do DP for 8.1 on the icon, which i'll help him with.
Htc updates
No to discredit the phone but if you're concerned about the Icon not getting updates, I'd also be wary about HTC getting updates.
None of their original Windows phones have 8.1 presently and what's to say that the M8 will be getting any updates or getting in a fast enough time? You very well may be moving to a new phone that has the same problem. HTC has not proven to be 100 percent reliable with their updates for windows phone 8 nor their windows phone 7 line up.
Even the Windows phone 8.1 update keeps getting delayed. Whether that is HTC or the carriers, I wouldn't switch because the phone has 8.1 now. HTC has sold far less phones so it should be easy for them to update the small amount which is probably less than 1 million
What about any future updates? That could be a waste of time/money for you. I'd stay where you are. Keep the icon, stay up to date on all things Windows 10(and Windows phone 8.1) related to our phones and if you haven't heard anything by the end of the year or beginning of the year, then decide what to do.
Me personally...I wouldn't get rid of the icon just yet for an M8.
Personally, I am getting annoyed with Windows Phone in general and I am contemplating getting rid of it and going to the iPhone 6 for good. But I haven't decided yet. Too bad you can't go ATT, i'd sell ya my 1520 if I did
But nah keep your Icon...and if you want more unbiased replies, I'd try the general windows phone forum as the M8 crowd can be a bit....defensive over their phone choice and criticisms

Of course you could always edge up and get the IPhone(I use Att next, so I am thinking of doing that). Use the iPhone and see what is coming out in 6-8 months. But I wouldn't move to a M8 simply because it could wind up being the same situation.
Learn from the Windows Phone 8x users who have grown disillusioned and annoyed with HTC. I've read their forum and comments and a lot of them are saying "I wish i'd gotten a Lumia". Those are the kind of comments that make me wary about ever using a HTC product.
Hey guys, I need some advice.
I have the Lumia Icon (on Verizon obviously) running the Developer's Preview. It's a great phone, butttt I'm just sick of waiting for the Cyan update. I have a Fitbit that can't sync, as well as other devices that can't communicate with the phone. I know this is a Verizon issue and not Nokia/MS, but it' is so annoying. I have no idea when it will be updated.
I was thinking of maybe Edging up to the HTC One M8. This would solve my real Windows 8.1/Cyan update issue. However, I don't know if I'm doing the right thing.
I love the Icon's camera and the wireless charging. How much of a trade-off am I losing when I go to the M8's camera?
Also, If I Edge up now (I Edged the Icon), then I'll be in Verizon's new 75% to Edge up again contract. Do you guys envision a flagship Windows Phone coming to Verizon in the next 6-8 months? I don't want to switch and then boom, something awesome comes up.
I'd love to get my hands on the 1520, but I can't leave Verizon's service, plus I have 4 devices with them.
Should I wait out the Cyan update? Get the M8 now? Wait for the next great Verizon Windows Phone?
Any specific issues as to not get the M8?
Please help! I don't want to leave Verizon or Windows Phone, but this issue is driving me crazy. My wife's Iphone 6 is looking pretty damn good lately....