I don't have direct experience with Kubota's emissions systems, but I purposely bought a 2005
L5030 to avoid that ...
My experience with diesel emissions is with big over the road trucks, which the majority of or problems are emissions related, to be fair, we can go a year without a problem, and lots of tractor owners don't seem to have a problem with it, but others have had to open there wallet pretty far too!
One of the important things with the emissions controlled tractors, is you can't just put put around, they need to WORK, and build HEAT, and once the Regen starts, keep working it until it's done! Idling doesn't build enough heat!
For me to open my wallet to buy a tractor that's over 25 HP, it's gotta be 2007 or earlier, 2008 is the beginning of the transition to the various "tiers", 2013 is when they began with the standards mandated now ...
So ... I'd rather have a 2WD no emissions tractor, than a 4WD with emissions ...
Mines actually 4X4 and no computer, no emissions ... !