For people with first generation Evos/Epics, they will just need to upgrade on their own by the time the dual LTE/WiMax devices come out. Because 80% will be off contract by then.
The big deal will be for Evo 3D, Photon and Conquer device owners (and WiMax only devices still in development like the Samsung Galaxy SII). These folks will likely be less than 50% through their contracts. Only the people who paid cash for their devices will be off contract by that time.
Sprint will need to come up with a reasonable solution for these folks to upgrade. Because even if there will be no merit to lawsuits for these folks, they are going to be royally torqued at Sprint.
However, if you think about it, by the time dual LTE/WiMax devices come out, how much LTE service is going to be out there? Not much I'd guess. Maybe three or four markets if we're lucky.
Maybe what Sprint could do is when LTE goes live in a market, offer contracts users in that market upgrade eligibility. That way they don't have to take the financial hit of taking millions and millions of devices all at once. Its really only the people that have LTE access that are affected. If you live in a non LTE area, what does it matter if your phone is WiMax only? Most of us WiMax device holders never have had WiMax anyway.
What I think is the smartest move of all (especially since Sprint is likely buying out Clearwire now) is for Sprint to fully deploy WiMax and LTE together with Network Vision. They could then market WiMax as a Value 4G service and LTE is a Premium 4G service. Then install them both on every NV tower. Clearwire has 150MHz of spectrum. This could easily be done. And most of the equipment between WiMax and LTE can be used together under NV. Its not really that expensive to dual deploy.
Sprint's LTE is going to be deployed in 20MHz channels versus WiMax's 5 MHz channels. The LTE network is going to be about 4 to 5 times faster than WiMax.
So in this scenario, you let the WiMax-only device holders keep them as long as they want and upgrade whenever they want (at their expense). And eventually we all get WiMax and LTE and we choose which one to use by which devices we have. Since Sprint's LTE will be faster, they could even charge a $20 data fee for it, I suppose. And if we have the choice of using WiMax only, I'd be OK with the higher fee for LTE.
But this makes too much sense for consumers, so I'm nearly certain it won't be done.
So in the interim, I will not be upgrading my Evo. I love all the dual core processor units that are coming out. They are definitely better. But the Evo still meets my needs for the time being. So I will plug along until the dual 4G devices come along in 2012.