I don't think we're getting a new park anytime soon, and Disney's current approach to just shoehorn whatever the hot IP is wherever they can put it regardless of whether it fits is not the sort of thing that would allow them to design a cohesive park. That said, they'd be foolish to just not consider it if a compelling vision could be realized.
But some counterpoints:
DCA was explicitly designed to be more adult focused than Disneyland, and that was one of the reasons it failed and why one of the first things they did was shoehorn in ABL. As much as they have a large adult fanbase, they're not going to design a park with adults as the target audience.
The Marvel Star Wars gate wouldn't have worked, especially given what has already been built and Disney's mismanagement of both brands as of late. Combining those properties into one place only makes sense if you are absolutely certain they will be evergreen (Star Wars, maybe, Marvel, well...I'm skeptical that the highs of Endgame are ever going to be replicated, at the very least), and that Disney will do them justice (in my view, their track record is at best mixed to negative). And the idea of such a gate is often predicated on a thinly failed hope that if there was a Marvel/Star Wars/other big IP I don't like park, the two existing parks would remain "thematically pure" or devoid of things that don't fit or properties that people don't like and...that is absolutely not something that will ever happen with Disney's current approach to their parks. Nor would it have happened in a time of better Parks management, because there was (and would be, in any circumstance in modern corporate America) obvious pressure to use the brands in the parks in a big way as soon as possible, and adding on to the existing parks was always going to be easier, quicker, and cheaper than a third gate. It also assumes the ability of Disney to act rationally and deliberately in service of adding a third gate within a reasonable amount of time, which nothing the company has done lately has in any way supported.
People say that DCA needs more, and I agree. However, the bigger problem is that Disney from at least 2016 onward seemingly has no idea how to add anything to DCA without undoing something about the park that works, in addition to the inherently flawed foundation the park was built upon. Waiting for a perfect DCA before building a third gate is akin to saying (as many are, either deliberately or not) that a third gate will never come. And that might be your personal hope, as well as the hope of many others here, but realistically, as fans we should be, at least in a theoretical sense, rooting for a third gate to come eventually.
This is not to say that I think the resort needs a third gate any time soon, or that I don't agree that there are much more pressing issues at Disneyland at the moment. But ideally DLR would be working to build itself up to the point that a third gate becomes a reality, because a third gate done right should be a moneymaker. It may not ever get to that point, but it should be their long term goal, and they should be working towards it more aggressively than they currently are, even if that third gate remains a hypothetical pie-in-the-sky for the foreseeable future.