I wonder how much 486 code is so specific, that removal would improve things.
At first, I thought, removing i386 support (not 32bit support), that's strange, isn't the i486 and i686 support equal more or less.
But appearantly, whilst the 32bit stuff is technically still 'i386' at its core, there is weird stuff in the kernel to actually make it work on 80386 CPU's because of missing hardware features (thus emulating it etc etc) and since REAL 80386 are probably REALLY not used by physical hardware anymore.
As said above, 80486's are still in use and are far more similar to pentiums etc then 80386's isn't it A pentium was just a 80486 with some extra extenions wasn't it?
80286 actually missed crucial functions and while backports/hacks existed, it simply was even more crippled then many arm CPU's are now (only 16 bits for example).