BTC's value will stabilize over the long term, probably at the point when 1 Satoshi = $1. 
Then Bitcoin would no longer be usable in its current form, as the fees could no longer be paid.
Does anyone else believe in a great future for NEM (XEM) project? What event/new can affect the attraction of new investors?
The NEM Software CTO posted an article on the plans to refresh NEM NIS1 last month. There are four things in the roadmap, see below official Twitter post and link below.
https://www.twitter.com/NEMofficial/status/1348932876331610113
https://medium.com/nemofficial/the-future-of-nis1-2c170c38379e
I don't see anything that NEM could do better after the introduction of Symbol. On the contrary, Symbol also has features that would have long been expected for NEM. As I said before, I believe NEM will suffer the same fate as NXT after ARDOR was introduced.