again, droid x users will not be stuck. i get what you are saying. now let me clarify what i was trying to say.
when devs present newer versions we are presented with everything new from the base band to the kernal. .340 brought both new from .320 for an example. however what you cant do is swap out kernals without going to a new system version. and really there is no need. with apps like jrummy's droid overclock you get to choose your voltage and frequency thereby fine tuning the kernal to get the max battery life and performance for your particular device.
so yea, there has been a solution for months now
but lets be honest, by the time motorola stops rolling out updates most will be ready for a new device anyway (especially if you are still using an eris). if the x isn't for you get something else. thats the beauty of android...choice. but fear of lack of forthcoming updates is kind of silly. the x is currently verizons top dog and will be popular and relevant for quite some time.