If older firmware is removed from the boot ROM, it will apply to both MK I/II and XL/XL+ users. As an XL+ owner, I definitely want the ability to select older firmware to retain the sound of older presets while simultaneously being able to enjoy the benefits of new firmware.
As an owner of Mark II, I understand perfectly your point of view.
I will be very happy if I can keep on receiving (some) new upgrade at the price having "only" the last modelling version, but I can understand that the people like you who have paid for a "more powerful" AXE FX II (XL / XL+) with no boot memory problem would like to have all the possible choices available at any time.
I mean, new amps / effects together with older firmware.