4096 is the largest we could go and still support most hardware out there. The problem with that though is it creates an easy footgun to waste loads of memory. Zooming or scaling increases the resolution of the text object, and so starts rendering it at higher resolution sizes. A single 4096x4096 texture uses 64mb of memory. So conceivably you could have ten or so text objects, zoom in, and then suddenly you've used over half a gigabyte of memory. That can crash the game, result in bug reports, or just people going to social media to complain that Construct sucks, which is kind of understandable as it's not that obvious why it did that. A 2048x2048 texture uses 16mb of memory, which at least limits the damage.
So to avoid accidental exploding memory usage, I'd rather not change it. I'd rather try to understand more about what you're trying to do and why you need such large/high-resolution text objects without being able to use something else like separate text objects.