See here's the thing: there's also no reason to change our rules to cater to customs-reliant characters. I hate that term btw -- there is no such thing as a 'customs-reliant character'. Characters are only reliant on customs if you let them be reliant on customs. The metagames of more obscure characters especially are nowhere near developed enough for us to make a reliable assessment that they are actually customs-reliant. Instead, by allowing customs, we immediately simplify this and give characters strong tools. These strong tools are not balanced in regards to the rest of the characters' tools, so these characters actually have simplified options and less overall depth. A really good example of this is Donkey Kong, whose custom Up B gives him a fast OOS option with super armor that autocancels on platforms, sucks the opponents, and deals pretty high damage with the ability to kill at higher percents. This move on its own simplifies DK's game enormously by giving him a ridiculously good all-purpose option in neutral. The allowance of custom moves inhibits the development of the default characters, which is especially significant because there are still a lot of default tournaments, especially ones coming after EVO.
We don't just add customs in order to make certain characters better, though, that's the thing. I suppose I should add an amendment to what I said.
There is no need to cater to DLC characters if it means experiencing comparatively greater losses.
Yeah, it'd be good to have the DLC characters viable, but allowing customs makes it so:
-Vastly increased character diversity (more than if customs were unallowed)
-Increased diversity of play styles due to the switching of custom sets (most characters do not have a single ideal set)
-More tools to experiment in the meta with
-Another way to make Smash 4 unique as a competitive game, giving it a strengthened identity.
This is not even mentioning
-Ryu (and maybe roy/lucas) will be viable anyways
-If the DLC characters end up getting customs and we have to reimplement them all over again after we got rid of them we'll just end up feeling like idiots.
In short: We don't lose anything by not getting rid of customs. This will be true no matter how many DLC characters we get, because they will do nothing but add to the customs on meta, or at the very least be benign as long as they aren't overpowering, in which case a customs off meta will just be worse. No matter how many are added, they will not take away. There will have to be
A: A lot of DLC characters
B: None of them ever getting customs
C: All of them being unviable without customs
D: Them becoming perfectly viable with customs
for getting rid of customs to be anything but harmful. None of these conditions have been met (except for B, but there's evidence pointing towards the possibility of customs for them).
Damned if you get rid of them, not damned if you don't. Therefore, keep customs.