Its important to understand, and thus for me to reiterate, that the D&D "basic" PDF is:
a) Not just a "quickstart" product. It is the complete core rules of D&D, which will be used as the sole basis for all future D&D products; it will contain everything you will ever need to use any future D&D adventure or sourcebook.
b) Not just an "SRD". A system reference document for rules is very nice, but it's not set up to be used in play. The Basic D&D PDF will be a free pdf RULEBOOK, not a reference doc. The intention is that people will certainly be using it to play D&D.
Some people accidentally or intentionally continue to mistake the Basic D&D PDF with either a 'quickstart' or an 'srd'. Some people continue to wish to claim it is just a gimmick; many have said "sure, it has all the rules needed, and technically it might be true that you could 'play D&D without ever having to buy a rulebook'; but seriously, does anyone think people will actually PLAY D&D with just this product?"
So here I put my Prophet Hat on, and say that in fact, the answer is YES.
I predict the following will happen:
1) There will in fact be quite a few people who will play D&D using only the Basic PDF. Particularly old-schoolers or people who prefer a more basic style of game.
2) In fact, I predict that people will take the basic PDF and create
modifications for it that are totally different from the 3 rulebooks.
3) People may form communities (or use existing ones) online to exchange such ideas and modifications.
4) We may very well end up seeing a bunch of 5e D&D Basic "Clones", or more accurately "mutants", which will take the core D&D Basic PDF rules and add and change them in weird and unexpected directions that the designers could never have envisioned.
5) This is less a prediction than a hope: if the above is true, and the people at WoTC have any brains, they'll actually ENCOURAGE all of this, and keep a close eye on what's created, to see what can be brought into the official product. It may even be a way to look for talent.
So there you go. Am I sure it will pan out that way? No. There's all kinds of things that could modify the situation; but if Wizards does everything right, and gamers being gamers, I expect that point 1 is extremely likely to occur, points #2-4 fairly likely.
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