I think 4 stroke is very likely to happen.
Personally I like the added tuning potential and great noise. I have been working on my own 4-stroke engine for a while (7.7cc DOHC, so higher RPM capacity). To test the principle I have fitted my buggy with an ASP 56 4-stroke. I'm soon going to start running it.
Clutch and gearing issues are pretty easy to overcome. Oiling as Mark has stated is not a problem, piston ring blow-by lubricates the bottom end from oil in the fuel. One big issue is heat, these run a lot hotter than current racing two-strokes. Both because of the extra friction and the fact they don't blow most of their fuel straight out of the exhaust, taking the heat with it. The plus side is they are much less thirsty and cheaper to run.
Here's my set-up.
Although this is still a glow set-up, I think the holy grail is going to be spark ignition petrol. That's my target for the 7.7cc engine. Glad to see HPI has got the petrol idea coming in their 2-stroke.