People have discussed sidechains and pruning and other suggestions, but the fact is, they will take time to implement to make sure they actually work. A 20MB blocksize is a far more simple solution that will work right now and until I hear something better, that's the one I'll be supporting.
Ok, but, see, we can go for 2-5-8 MB limit (wihtout exponential growth) before we hit the limit, and use the time gained by shooting the can to invent something better
It's not so urgent that our only choice is to implement exponential size growth
What you are saying now is, let's go exponential, maybe we can sustain it.
This is the worst anti-fork argument, since it means you'd want have to have another hard fork each time you need to increase it. If exponential adoption happens, either we find a way to cope with it, or another coin will. Again, there are only two outcomes. Increase the limit, or jump ship when Bitcoin can't cope and grinds to a halt.