Yes. We are doing exactly what you described in your last paragraph.
The HTK is never linked to simon - simon starts the htk executables during the building of the model which makes it _perfectly_legal_ (if starting proprietary applications from within other applications simon would not be allowed to start say MS Office either).
All HTK specific code is bundeled in the simonspeechcompilation library (in one class) which could easily be replaced by a GPL replacement - if there were any.
The same goes for Julius, btw.
The server application is called simond and uses tcp/ip. Audio streaming over the network is supported. As only the server uses the HTK you could do a huge setup of simon with one main server that compiles the model thus further limiting the need for the HTK (it only has to be installed once, on the server side).
As we neither have the know-how nor the resources to re-write the HTK this is all we can do for now, sadly.