Well I guess that's going to be good for those "cast [insert arbitrary number here] of [colour 1] or [colour 2] spells" if you can have enough vigilance creature to keep the game going until you complete the quest.
You kinda hit the nail about why it's gonna be a pain. If the opponent plays cards that break the rule no big deal BUT you opponent can also play in a way to not give you that information and so you have no idea. Let's take the dual caster here and say your opponent has not cast cards with the same name how can you be sure the deck is singleton (except in singleton formats obviously).
If I'm not mistaken Thoughtseize will be the only tier 1 non-creature spell from Modern and Legacy that's legal in this format.
Actually, I'll go over the colors real quick looking for what they lost and kept compared to Modern and Legacy.
Red has lost probably the top 3-5 spells (Bolt, Looting, Chain Lightning, Forked Bolt, etc). We're literally talking Shock / Incinerate level now.
Blue has lost all existing cantrips as well as Jace, Delver and Snapcaster.
Green has lost its top 3-4 mana dorks and its top 3 tutors (GSZ, NO, Chord), only leaving Company behind. They also lost Goyf.
White has lost Path and Swords as well as SFM, which is already all the cards that ever made this color playable in eternal formats.
Yeah, I think I'd start brewing with black first... I think WotC will end up regretting reprinting TSeize in Theros. It's on paper the best spell in the format by a mile.
And that's the saddest part of Pioneer. Once all the cancer that needs to ban will be gone BGx deck will probably become the dominant deck in the meta and will end up like pre up Jund modern just less powerful. Although I guess some ppl will rejoice at that.
On one hand a format without fetches could be nice for the way cheaper decks but this does not change what others have pointed out WotC don't reprints in sufficient numbers to keep up with players demand. Let's all see in 5 years how expensive Pioneer has become.
And that's the saddest part of Pioneer. Once all the cancer that needs to ban will be gone BGx deck will probably become the dominant deck in the meta and will end up like pre up Jund modern just less powerful. Although I guess some ppl will rejoice at that.