well, I guess it will only be worth the investment in airports where the taxi is very long, engines have limitations in this respect , you can't just start the engines and start the take-off roll, they need time to warm-up, the type i fly requires a minimum of 2 minutes, and that is if the weather is not too cold, if it is too cold you may have to increase the warm-up time before you can start the take-off.
Then you have the issue of providing ventilation, and Some aircraft have no APU, on some others the APU does not provide bleed air , or the APU may be not working, even if you do have APU, it is already burning fuel.
You also need a electric power source for vital systems to work, and that would be too much for batteries fitted in most airliners.
Some companies taxi on 1 engine and no APU untill approaching the holding point to save money.
It would have to be planed together with aircraft designers, so aircrafts built in the coming years have some sort of standarized electric driven ventilation system and the towing machine should provide electricity, a sort of mix of a GPU and towing vehicle all in one. But even then, imagine the queues it would create (the thing would have to stop, disconect the system, then move away, of course the crew would start engines with no ground visual indications or feedback, etc etc), also the price of the service is possibly higher than the fuel burned on taxi, at least at current fuel prices.
It does not surprise me it is a German company the one studing it, they have a specific tax for aviation fuel in germany, and itīs quite a high one, can't remember the exact percentage,
AFAIK only german operators pay it if operating to/from/within germany, foreign companies do not pay it.
I do not see it as something happening in the short term at least, but that is just my opinion.
I will be interested to see what the future will bring in this automatic assisted taxi system.
LEVC