Ok Guys, some wild thoughts from 'left field' - please excuse if you have already thought of them
ModelsI would tend to treat them like drop pods and DeathStrike launchers respectively:-
Termites (and any other 'disposable' vehicle) can be kept on the table for 'scenic' reasons just like Drop Pods (I also use mine to assist with placing the relevant formations).
'Launchers' could be retained as real vehicles and activate as such. Providing they are still on the table they could provide guidance to the tunneller removing the need to scatter (see below)
To launch or not to launch(or there is no such thing as a free launch
)Hellbore (and other major assets:-
Treat the Hellbore like a kind of one-shot WE 'missile', the bare launcher as an AV. The Hellbore has 0cm movement (but can tunnel) while the launcer has perhaps 15cm??
When the 'launch' activation is successfully declared, The player records an
unmeasured guess at the exit point of the Hellbore which can travel up to perhaps 50cm per turn? When entering the table, if the estimate is over the speed limit and the Launcher has not moved, move the notional exit point back in a straight line towards the launcher.
Disposable vehicles and underground Tyranid swarms start off-table, and take a while to travel - so arrive in turn #2 at the earliest. Their entry point is plotted at the start of the game like spacecraft.
They have to 'activate' to arrive, and may declare an assault, but the scattering process may result in them ending up out of reach of their intended target.
ScatteringI think all unguided formations should scatter 3D6 in a random direction. This simulates tunnelling through rock strata or the availablitiy of tunnels in the right places. (Note I am not suggesting that the player gets to move the exit point first like the Drop pod rules).
WE whose launcher has not moved do not scatter, but my arrive up to 15cm from their intended exit point. The WE must activate to arrive
Enemy formationsUnless assaulting, tunnelling formations may not arrive in the ZoC of enemy units. The opponent moves the exit point the minimum distance to clear the ZoC.