You should be clearer with your question next time and not be so vague if you wanted some specific answer that nobody probably has the answer to.
As for now, the word is those who got WP8.1 should get W10, just not all the functions as some hardware won't be able to handle it. Which means unless you have some odd phone you should get W10.
That also depends if your carrier allows a release but I suspect that a developers preview like thing will happen which will allow phones to update regardless.
I don't see MS treating WP like Android gets treated. However I think this is probably the last update for WP8 first gen phones IMO.
Your initial answer spoke to the state of the Windows Phone ecosystem once Windows 10 for Phones is released, which is it's own thing that has already been covered in the media I was wondering if anyone knew what may happen with the old software, as I only check Windows Central, but it appears to be anyone's guess at this point.
I would like to see something happen to Office on 8.1. But, if Microsoft is done with 8.1, as you've suggested, then we'll just have to deal with it or upgrade. The newer phones are $100, so it isn't that much out of pocket.