The starter motor is unlikely to be an issue, especially if a hi output 4 brush ball bearing type is used. A 4 brush type will have no trouble coping with that load. A strong battery and heavy leads are obvious requirements.
The backfire device would need to be carefully adjusted to ensure it does not "go off" when attempting to start the bike, but that also the "shock absorber" dynamic that it provides is not overly lessened. The actual named feature of the device (backfire) is not really a concern if a digital ignition is used, like Tri-Spark (or Pazon, etc), as the Tri-Spark for example never kicks back.
The sprag clutch barely cuts it in a lazy stock motor, so it is likely that any wear in that area will reveal itself sooner rather than later if more is asked of it. The potential solution there is the Alton replacement starter drive for mk 3, but as has been mentioned before, that is not quite to market yet. It has a much larger sprag, which promises to be much more robust, and likely to cope with higher loadings.
The Alton starters for pre Mk 3, which are now generation 3, have strong and sizeable sprag units, which work extremely well. A similar set-up adapted for the Mk 3 promises to work equally well.
