Avgas is a 'leaded' fuel, seen as very 'not' environmentally friendly. All manufacturers looking to produce a "lead free" option. No Avgas produced in UK these days.
The environmental issue is actually a non-issue, as worldwide consumption is so small as to be environmentally irrelevant and it's also destined to get smaller and smaller as GA more or less dies off, or moves to ultralight planes that simply use mogas with no issues. The problem is that as production decreases the production costs really don't and it becomes economically no longer viable, leading sooner or later to cessation of production.
As to the original question, I doubt we'll ever see turbines small enough to replace Lycosaurs and Contisaurs actually certified and fitted. The certification costs alone for such a small market would put off even the most risk-prone manufacturer. The small jet turbines the OP has mentioned that are used in gliders are not certified and can be operated only as sustainer engines, they're not allowed to autonomously take off and most couldn't even pull it off for performance reasons.
It will be a lot cheaper and easier to develop certified piston engines that can simply run on standard mogas, which will still be available for some time to come. They will also have the added advantage that they won't require your average PPL holder to get a turboprop rating to be able to operate them, they'll just be another (more modern) type of piston engine.