We have that in P3D, because there we have SODE jetways, which provide this feature as standard, with a separate animation for the stairs.
The MSFS version uses standard jetways that, while they look very good ( since our P3D models we already 100% PBR, so they look even better in MSFS ), are a bit more limited in what they do, for example we don't have gate with double jetways and with both jetways working. We'll probably look more into that, once Simconnect will be fully featured ( right now is incomplete, not all functions are active ) and we'll get better chances to controls object animations with custom code.
