FWIW, I’ve just installed Haiku Beta 4 on MacBook Pro 2015 (Model ID: MacBookPro11,5).
I had to use the rEFInd boot manager, and the “Use fail-safe video mode” boot option to be able to launch from the USB installation stick (it was also quite tricky to enter the boot options, I had to quickly press “Space” key several times right after I select Haiku USB in the rEFInd). For whatever reason after the first successful USB boot the UI was in Spanish, so I needed to blindly change the language settings (luckily the globe icon helped to find the right item).
I reformatted the 16 GB FAT32 partition to BeFS via DriveSetup, but for whatever reason it refused to change the partition type from Microsoft basic data partition to Haiku BFS, and I had to do it manually by rebooting into the Mac Recovery Mode deleting the GPT entry and readding it with the correct partition GUID (42465331-3BA3-10F1-802A-4861696B7521).
The Installer doesn’t add the haiku_loader.efi to the ESP (EFI system partition), so one has to copy it manually from the USB stick following the UEFI Booting Haiku instructions. I’m not sure why Installer still doesn’t handle such a simple operation by itself. There’s a 5-years old Trac issue #14967 which aims to handle all of UEFI installation corner cases, but IMHO most of the users would be happy with just the MVP solution suggested by @kallisti5 in one of the comments (as an engineer who embraces pragmatism I can’t agree more with his last sentence there: “You don’t eat an elephant all at once. It’s one bite at a time”).
Nevertheless, after a few hours of trial and error I now have Haiku running natively on a MacBook. Isn’t that awesome? 