IMHO the BOI/LTR visa range is pragmatic and comprehensive. Their only weakness is the availability of redundant offers such as OA, OX Elite, etc.
As far as retirement is concerned the LTR should become the only long term option, while extended tourist visas (3 or 6 months a year) could be offered to retirees. Of course people established under Non O and Non OA, etc should have the possibility to remain under their current conditions.
Now that leaves out the Marriage option, which the Thais will probably leave as it is now.