For me, since my funds are in either the single or joint account in any given month, it will not be possible to earn the maximum EGA bonus and Everyday+ 1% every month under the new terms.
For example, if I register my joint under the BTL promo, my joint will have a high Jan balance. Under these new terms where sole registration automatically means joint account registrations, registering (my sole) under the Feb promo will mean only my sole account can earn 2.8% +1% and for Feb only. In Mar, if I use my joint account, it will at best only earn the Everyday+ 1% interest because of the high balance in Jan. So, unless there are better alternatives, I will still use my sole in Mar and earn only 2.8%.
Assuming that this is indeed how HSBC wishes to run the EGA bonus promo going forward, then there will be one month when there will be zero balance in my bank accounts.
I think in order to be able to earn the maximum interest inclusive of the 1% every month under these new terms, you will need two sole or two joint accounts.