I'm not sure if this point has been covered but it may be worth ascertaining the views of your insurance company when considering to exempt or not
I'm also a member of the VJMC, vintage jap m/c club, which has published in this month's mag, some replies from insurance companies active in the historic vehicle field. The majority said that exemption is fine but reiterated it is an insurance requirement for vehicles to be maintained in a roadworthy condition. However, Footman james said, "We appreciate that vehicles over 40 years old are, in the main, cherished and maintained to a high standard by their genuine classic enthusiast owners. Therefore, we expect that many will voluntarily continue to have an MOT carried out on their vehicle, regardless of the change in the legislation". Personally, i will continue as before to get annual MOTs for both the bike and the van, mainly for peace of mind, but each to their own