There are a number of advantages to running SPort telemetry off a Teensy (or whatever) board. For one thing, you don't need special firmware for the AQ.
Updating the main firmware is always a tricky thing and consequences of bugs can be dire. With the M4 there is only one serial port anyway, so by using an external device to translate Mavlink to SPort, you can still keep Mavlink. Also you need a converter between AQ and FrSky Rx, and the only way to do that "off the shelf" right now, that I know of, is to use 2 somewhat bulky adapters which are about the same size as a Teensy anyway (the signal needs to be inverted and AQ Tx + Rx combined to one wire). There were some tiny adapters in the works at one point, but I'm not sure what their status is right now.
I'm totally pressed for time right now and probably will be through most of July, so I wouldn't expect much from me in the short run on either front.
If Norbert can get the MTA stuff I sent him working, that would be my personal recommendation for now since it is geared specifically for AQ at the moment (flight modes and such).
-Max