To put it to you simply, that is possible but you increase the workload by 2fold or more. Java is hard to explain or understand. It takes a lot of time to get stuff working and also java is very powerful. In the same way that no one teaches people how to do FMs and stuff, java essentially has the same effect. Frankly I'm confused why it is possible to find out how to do the java class files but so much harder to find out how to do FMs. The class file controls what FM it uses, can even edit the FM and also controls what weapon loadouts you have, how much ammo you have etc... So in effect I'd personally say knowing java is a much more powerful tool that knowing how to do FMs... but I guess that's not how most people see it anyway.
Teaching someone isn't the simplest of things so it's more work for us and also for the guy learning they are bound to get it wrong on the first couple of times and then in practice from my experience the guy who is teaching him will end up doing the slot for him anyway. Also the current requests such as float plane slots aren't exactly the simplest of things and have a lot of other well stuff tied up in it.
Then it depends if the guy really wants to learn it, look at it like maths. Some won't mind it, some will never understand it however hard they look at a problem etc... There are some talented modders out there such as ranwers for example. He has access to class file tutorials and if he wanted he would only need to ask to be taught but he hasn't decided to learn it. Why? Well I can't answer that you have to ask him but the usual trend is people specialise in their certain area. For ranwers this is hier.him file editing, making frankenplanes etc... Some do new 3D work, others do java and the remaining do FMs.
If there was someone who wanted to learn about java, depending on who it is and their reputation, what they have done so far then they may be taken up like an "apprentice" as such by one of the modders and taught...