The 303 will never actually come back, the closest you're ever going to probably get is a x0xb0x unless Roland can make some sort of deal to use Moog's patented filter which they stole until Moog's patent actually went through (which is my main understanding why they haven't brought back an authentic rebuild despite the demand).
Diode ladder filter vs transistor ladder so not the same at all. Not sure what you're talking about.
Maybe you're thinking of the arp 2600's filter, they got in trouble with moog for copying the moog filter design and had to start using a different filter.
I'd say the main reason they never brought the 303 back is that it was a huge fucking failure. As a commercial product it bombed hard.