It comes when it comes. No biggie. Nexus One and other phones can get 2.x first because they don't use proprietary addons.. (HTC Sense). Hence why almost every other phone is rooted quickly. You can definitely wipe out the Eris and put something else on (different rom) but then you lose the HTC Sense.
Verizon can bring the Nexus One possibly before Eris gets 2.1 because 95% of the people that are already on the Eris, will not be looking to switch phones since they've invested money into a phone and are now out of a free upgrade and probably not willing to spend $200-300 on another phone.
it will come when it comes and no sense in getting frustrated. Q1 is still here for awhile.