Here's something to consider.
Veteran contracts are based on years in the league; a player with 5 years of service is guaranteed a certain amount, a player with 6 years is guaranteed more, etc.
It's possible that with the hard cap, veteran players might see their ability to play on contending teams severely curtailed.
If you are an 8- or 9-year pro, you could be forced to choose from a bunch of rebuilding teams that have cap space, instead of a contending team that actually wants to sign you (and for whom you want to play).
When all these amnesty-types hit the FA market, it's possible that no one may be able to sign them.