Maybe the Question Should Include "Any Further"
Personally not a big fan of MPL, but I'm also not a big fan of "frozen ATPL."
Some clarifications. The MPL is not recommended by ICAO. ICAO merely requires that it be recognized as a valid license for intl ops. There are plenty of CAA's that haven't approved MPL in their own licensing schemes, and haven't indicated that they're close to buckling under to any industry economic or political pressure to do so.
And it's not "no flight time," but merely another reduction in required actual flight hours. Too lazy to look it up in Annex One, but I believe there's still a core flying component of around 100 hours that has to be accomplished in an actual aircraft. Personally, I don't think there's a tremendous difference in piloting skills between a 100-hour and a 250-hour TT pilot. It's really the brainwork that's being expanded in that timeframe, along with a bit more precision that the repitition of the mechanics of flight will give.
Add to that the fact that MPL's receive an additional 200-400 hours sim training on-type, and it's arguable that they will be better qualified than the 250-hour right-seater.
One the safety side, if anything, you can take comfort in the fact that they won't be conducting any commercial operations without adult supervision (right-seat on MCA and no single-pilot ops). And you won't be dealing with them punching holes in the clouds in a Cessna, Piper, or Diamond for anything but supervised training.
On the employment side, it could be said that candidates going that route are trading their future job prospects for a shot at the Boeing or Airbus. Since this was an idea pushed by IATA during a boom-in-growth period, it will be interesting to see how much traction and acceptance it manages to gain and maintain during the period of slow-no growth or service reductions. Its attractiveness to the carriers will remain low cost workforce, lowered training costs, and an even greater measure of indentured servitude than they enjoy with the sponsored ab initio crowd.