In article TonyV writes:

There are some hopeful signs in this direction. The general aviation
press is starting to talk about FADEC
(http://en.wikipedia.org/wiki/FADEC) retrofits for the general aviation
airplane engine. If, as is likely, 100LL fuel is to disappear, the
larger engines will require some type of electronic engine control. Off
topic, I know, sorry.

And we will probably lose a bunch of the GA fleet with engines that cannot
be modified at an affordable price. This will probably include a lot of tow
planes. The others will need to pay for the new engine or new engine controls,
and you can expect that to add to the price of tows.

As long as they last, the dinosaurs are doing the job. 30 years ago the
Cessna could haul me 400 miles each way for a weekend without a problem.
Nowdays it still can (except for the frightening price of fuel to do the
trip). For that purpose, the glider has not caught up.

Alan