Personally, I will never need SnapChat and would never use it if it were available. However, I think once Windows 10 starts taking off and has been rolled out to Desktop, Xbox One, Mobile, Tablet, etc., I think SnapChat would be rather fooling to continue to ignore the issue, as it would be easy for the sheer number of Desktop/Xbox/Tablet owners out there to start searching for an alternative. Once these users start using an alternative on their other devices, they'll want to switch to that alternative on their phone as well, and SnapChat will start losing ground very quickly.
Is it definite that this will happen? No, but it is a real possibility that SnapChat would be foolish to ignore. Microsoft scoffed at iPhone when it came out and looked where that go them. Microsoft won't be making mistakes like that again.
As far as "is it good for the platform", I think there are a number of apps that need to come to the platform in order to attact iOS and Android users both, and SnapChat is just one among many that are needed to make that happen. Better video editing, more banking apps, apps that are more complete and not dumbed down copies that don't have the full functionality of other platforms. With Windows 10 universal apps, it will be possible to begin to overcome all of these issues. A video editing app made for Windows 10 Desktop that can be also used on the phone has the potential to be way better than any other offering on other platforms.
Banking apps also have the potential to be much better, considering you'll be able to take pictures of checks from your phone, tablet, laptop, desktop, etc. Even use your all-in-one printer/scanner to scan checks. That would be nice for businesses, as they could use a printer like I have that has a sheet feeder for the scanner to put a stack of 50 checks on the scanner, and scan them all to a bank deposit. Yeah, it scans double sided due to the ability to flip the page after scanning one side. That would be a boon for electronic banking and convenience of businesses. It would also cut down on the amount of work needed to be done by humans to work those large deposits with a lot of checks by hand.
Sorry if I'm sidelining SnapChat, but the reality is, there are a lot of apps people are waiting on. While for some, SnapChat is one of those apps, for others, well, there are just many apps that need to be added or completed or debugged.