Netsurf GUI needs an intuition port if possible, also WarpOS would be nice.
The OS4 version has a Reaction GUI - it shouldn't need much tweaking for OS3.9. There are other code parts which are more OS4 specific and will require retro-fitting.
Somebody who has the time and knowledge to look through it probably wouldn't have much trouble back-porting it to OS3.9.
But it's still a RAM eater, so it wouldn't help me much.
There's a caching bug in the current versions - a fix is being worked on.