MLS has already solved this problem, and I won't be surprised if the ESL eventually follows suit. Basically MLS allows clubs to gain first dibs on players who don't or haven't played in MLS, haven't previously registered for their SuperDraft, or aren't U.S./Canadian national team players (includes underage sides).No, not necessarily. The NHL for example has a draft age that precedes college, and the vast majority of its draftees are out of the Canadian Major Junior Leagues or Europe.
I agree an entry draft on the NA model seems a feature that would be hard for a SL to adopt. But you could imagine for example a system where you have a draft to distribute the rights to players in non-SL clubs, but with the possibility to sign young players below a certain age for development in your own system. Combined with putting player movement between SL clubs on trade basis rather than for cash.
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