Bolt in cages are designed to be bolted in. Weld in cages are designed to be welded in. Both as individuals are currently allowed in competition
In a vehicle such as the 205 when/if the time comes to sell, if its been done right from the beginning its retail market will be double, as it can then be used as either a track or competition vehicle. If it breaks the rules the market and price drops considerably.
With such sad events like what happened recently on the Rally of Wales, we constantly expect knee jerk reactions from the MSA, roll cages could be one of them. Okay so this car may never see a competition but trackdays and other types of non competitive motorsport will be getting more strict in the future due to insurance reasons and this is one area they could look at.
Do it once do it right.