Frankly, transfers are the expected meaning of those bids, and "to play" 2M over 1N is hardly played by anyone anymore, and those that do are usually playing some sort of weak NT. I think the "to play" bids should probably be alerted, and don't have much sympathy for anyone who assumes an unalerted jacoby bid is to play. I think the situation is similar to 2♣ opening. The strong version that 99% of players play isn't alertable (at least in the US), whereas the less common but NATURAL means (e.g. Precision or EHAA natural 2♣ openings) are.