"Starting with this set, all planeswalkers past, present, and future will have the supertype legendary. They will also be subject to the "legend rule." The "planeswalker uniqueness rule" is going away. What does this mean? In short, everything that's true about legendary permanents will now be true about legendary planeswalkers."
"Under the new rules, if a player controls more than one legendary planeswalker with the same name, that player chooses one and puts the other into their owner's graveyard. This means that if you control Jace, Unraveler of Secrets and cast Jace, Cunning Castaway, both Jaces can exist under your control."
This means that you can have any number of identical nonlegendary planeswalkers! And I can finally try to make my ability-spawned planeswalker idea!
Which brings me to @mtgcardsmith
This update will hopefully prompt you guys to work on the new planeswalker builder. Along with 4th ability capacity and everything else already asked for, I'd like to strongly suggest making Supertypes either optional/selected like in the M15 builder or completely custom like Subtypes are.