There is a reason why Apple includes this with every installation of OSX...
https://support.apple.com/en-gb/boot-camp
At worst it's a minor inconvenience for most, Apple already provides the tools to allow their customers to run Windows & all it's programs.
A Windows 10 license can be bought off Amazon for the price of a couple of pints down the pub & remains perfectly functional even if you don't pay for a key.
Players that have bought ED for Mac already have a PC license (& vise versa) so no extra cost there. In fact there is little to no extra cost to the player other than their time to set up boot-camp & install Windows + EDH. The chances are most of them will already be using boot-camp for one thing or another so will probably already have the system set up.
The only people that might be locked out are those that were on systems that were only just able to run the game in the first place. Or, (which is more likely) those that simply don't want to use the tools provided to them (but that is all on them).
That said, it would be a nice gesture of goodwill if FD offered those that might be affected by the change access to Horizons, either via bootcamp or their console of choice.
If it helps any Mac users out there, I played over a year of ED, including a ton of cross-continental PvP and Horizons, on an iMac using Bootcamp.
I don't know much about computers but I never had any problems.