Everybody is free to contribute what they want to Dolphin. If somebody capable wanted to implement such features, i'm sure it would be welcomed with open arms.
I don't understand the problems with cache emulation to know how complicated it would be to properly emulate any of them. But generally, the developers invest their personal time on issues that are interesting to them. And what is interesting differs from person to person. Some would weight the ratio between effort and results between different features, some just work on issues on games they care about, others just like the challenge. And then there's the JMC factor...
I don't understand the problems with cache emulation to know how complicated it would be to properly emulate any of them. But generally, the developers invest their personal time on issues that are interesting to them. And what is interesting differs from person to person. Some would weight the ratio between effort and results between different features, some just work on issues on games they care about, others just like the challenge. And then there's the JMC factor...