Good post. USL probably will get Tier 2 Status, leaving no Tier 3 league in the USA. The NASL will not get on board with USL because it is in direct competition thanks to the links to MLS.
I think the NASL doesn't exist in 5 years. I have no clue what the Cosmos, Miami FC or SF Deltas will do then, but I think the league will go.
The USL is managed better and MLS is willing to help it along.
They could be done, and done fast. Pessimistic timeline prediction:
2016/17 - USL granted D2 status
2017 - Chicago NASL goes on hold due to continued lack of viable stadium deal
2017/18 - Rayo OKC folds
2017/18 - New York Islanders receive approval to build new stadium at Belmont Park
2017/18 - Canadian Premier League (CPL) officially announced, will begin play in 2019 with Ottawa
2018 - Jacksonville, Indy, Carolina, and Tampa announce plans to move from NASL to USL for the 2019 season.
2018 - Edmonton announces move from NASL to CPL for 2019.
2019 - Cosmos, Miami FC, Ft. Lauderdale, Puerto Rico, and San Francisco announce the NASL will not play the 2019 season; league folds.
I'll set the over/under at 3.5 more seasons of NASL. Revise down to 2.5 if USL gets D2 status by end of 2016. I'm expecting that mass exodus of teams that want to exist at all costs (rather than the ideological organizations like the Cosmos and Miami FC) extremely soon after.
EDIT: Oh yeah, this is the stadium thread.
2020 - NYCFC announces stadium deal!
2025 - NYCFC plays first game in new stadium on 10th anniversary of team's first game ever