What is wrong with multiple solutions?
I think that is the only issue here.
It is indeed a deep, philosophical question. It is partly my sense of elegance and economy, not to needlessly multiply entities. I'm not sure if I can explain this aesthetic to someone who doesn't already share it, though. This isn't to say multiple solutions are always wrong; rather that redundancy needs to be justified.
If you like AT, then use AT. If somebody likes SQL based then they SQL. If someone want to do FSM, they do FSM.
Nobody said you had to do all of them. If one works that is good enough.
Every node that validates transactions has to implement all of them. Everyone who works on Nxt core has to support them all. Everyone who writes a tool that works with blocks; everyone who wants to read a transaction and know what it is doing. Once in, they must be part of the core forever (else historic block-chains can't be verified). I think it's great that Nxt can support multiple solutions, really I do, but I also fear an accumulation of crud and bloat.
(PS I'm off to bed now. It's 11pm in the UK.)
I have bad news for you if you dont like redundancy.
Blockchain is redundant
Even I dont need to know about every API NXT has, and I think I am one of the more active users of NXT API. NXT is modular so as long as the modules are not depending on each other, then there is no need (though of course desirable) for core devs to know all the details about the other modules. That is why it is called modules, modular.
Anyway, NXT is decentralized and nobody can stop anybody from developing additions. The way I understand it, a new tx-type gets its own handler and it lives in its own universe. Granted each tx will use a bit of CPU on all the nodes, but so far the CPU usage is minimal and moore's law should be able to keep the percentage used to the current type of level
So dont worry that NXT will get too many languages