I had a car MOT yesterday and I was speaking to my friendly MOT tester about this. Apparently the extra items should be tested as of the 1st of January but don't actually come into effect until the 1st of April. Between now and then there will only be advisories for the 'new' tests.
I can't see why remapped ECUs will be a problem. Most of the extra or new tests are things which I thought were already tested. All dust covers (e.g. for ball joints) must not be split. Inner CV boots will be tested (apparently before was only the outer ones
). Batteries must be secure and MOT testers are advised to remove any battery covers to check but only if no tools are required to remove the covers. Power steering pipes will be checked for damage and/or leaks. Instrument cluster lights must work; that's both the illumination lights as well as warning lights. Years ago a friend's BMW failed the MOT because his speedo illumination was not working and I had a car fail because the ABS light was on. But now SRS or seat belt warning lights will be checked and even traction control switches and lights will be tested. Seems to be a case of "if it's there it should work" which makes sense really. Mind you I might change my mind when I take one of my oldies for an MOT test in a couple of weeks.