I've heard no rumblings about the MSA bringing in tyre restrictions for Cross Country Trials, Orienteering, etc.
I have heard club members muttering about how the people who drive tricked-up vehicles, with super-aggressive tyres, are stopping them from doing will in RTVs & Tyros (not 100% sure how someone else's vehicle-choice can stop you driving well) and we should ban aggressive tyres in RTVs (which leads to all sorts of "interesting" problems & knock-on effects that the grumblers never want to actually address).
My recommendation for anyone coming to join RTVs (or Tyros) and want to buy new tyres is to buy something like a BF Goodrich Mud Terrain or an Insa Turbo Sahara [mud terrain]. - they have good road-manners as well as being very good off-road tyres.
Once you've worked out what you actually want to do, you can consider more/less aggressive tyres for the future.