Proposal: Magic: The Gathering
Draw3Cards currently has 557 tags about Magic mechanics, sets, etc. Could this be integrated into the Board & Card Games SE sites, or is this enough to warrant a new site for a Magic: The Gathering SE site?
Right now, D3C—a SE 1.0 site—has 558 tags. But…
There isn't necessarily a 1-1 correlation between tags on a SE1 site and a SE2 site. A major factor in that are synonyms (new in SE2), which helps a site do without a fair number of tags. Does a MtG Q&A site really need separate tags for tap, tapped, and tapping?
D3C has a large number of single-use tags—over 200 of them. If a tag is only ever used once, chances are it's not a very useful tag.
Many of D3C's tags can only apply to questions that would be closed on a SE2 site; e.g., "subjective" and "speculation."
Many of D3C's tags can only apply to questions that would be on a SE2's site Meta; e.g., "meta," "moderator," and "faq."
Many of D3C's tags can apply to other games besides MtG; e.g., "rules" and "strategy."
Right now, Stack Overflow has nearly 30 thousand tags (not counting a couple of thousand synonyms). The SE platform can handle a lot of tags without breaking a sweat.
And so on…
The end result is that 558 tags may sound like a lot, but nowhere near that many would actually need be added.
So (finally) to answer your question:
Does MtG require so many new unique tags that bcg.se can't handle them all?
In my opinion, no—not even close.
Instead of trying to guess whether or not MtG content would be welcomed on B&CG, why not find out? Ask good questions there, tag them in a way that's consistent with the site's expectations, and see if that meets your needs. If you run into a problem with the way your tag requests are handled, try to work it out on meta.bcg.
If after all that, you don't feel that B&CG is handling your content the way that you had it on D3C, then you'll have evidence that Magic questions may not work well on that site. (You may want to separate issues that are specific to B&CG from issues with SE sites, though ... it may turn out that it's not possible to fit D3C's content into a SE 2.0 site.) And if it doesn't come to that, you may find that whether or not there's support for a standalone 2.0 site, you'll have a home for those questions on an existing 2.0 site.
Looking at the tags on B&CG, the vast majority of them are tags for a specific game ("dominion", "magic-the-gathering"), while the rest are abstract concepts that might apply to all games ("strategy", "rules", "house-rules").
Compare this to D3C, where all the tags, by definition, define specific elements of the single game: tags for different sets ("Innistrad", "M12"), different variants of the game ("commander", "two-headed-giant"), the myriad different mechanics in a continually-growing list ("unblockable", "sacrifice", "level-up", "poison"), tags for steps of the game ("declare-attackers", "combat"), and tags for specific concepts of the game ("deckbuilding", "card-advantage"), among others.
While these can all be added to B&CG, they only have meaning in a discussion about M:tG and would otherwise "pollute" or at least seem out of place in B&CG's list of tags. Certainly they can't be applied to other games (even if another game has a notion of poison, it means something entirely different than what it does in Magic).
The point here isn't the number of tags, but rather that this wealth and depth of topics represented by the tags on D3C is a strong indicator that MtG deserves and needs its own site.