Ready.
With old floppies, you could boot your computer. Actually, you could do that in desktop computers, now, too (with CD/DVD, or USB-drives). That is convenient, but has security risks.
Tablet computers seem not so convenient for that, although they could be. Furthermore, getting rid of the security risks, is convenient, too.
Problem Statement: Personally, I thought of that in 2012, about when (Apr.28~,2012?), postman brought my first tablet (android @ DX), or a bit before. Firstly, before buying that, the wish to buy an Oberon Operating System tablet, was facing the reality that there was none such in the list, & furthermore, you could see that, there was a herd of "versions" of androids out there. Surely, one could "burn the ROM" with some Oberon code (if you would risk that with your programming/installing abilities), or some newer/newest download of android from internet, but that was hassle, risky, & presumably, lots of "diplomacy" to make various platforms agree (whether for fully replacing (without any "flashbaks" haunting you), or co-existing (pre-emptable within same disk) versions). Read all of their documents, & let some out, let other in, ...
What makes sense is just having the tablet firmware having ability to boot from the microSD-card slot. Furthermore, having (at least) two microSD card slots, makes sense. Then, you could modify the Operating Sytem in the writable (modifiable by applications) microSD-slot, and when you estimate that would work fine, then just pull out the microSD card that is in the OpSys slot, and insert the newly-written OpSys to that slot. The tablet does not have to have any internal SD-card. Having both of your microSD cards (OpSys, & data-&-apps cards) removable, means that if you are hopping them as a couple, then whatever bugs any of the other operating systems you try in that machine may have, that pair will never be exposed to any risk (that is, unless you forget one of your disks oplugged, while taking its couple out.
If your tablet also have internal storage, then the most riskless is to not allow that interact with the slot-borne one. In old times (1980s/1990s), people were warning you in published articles that you should keep away your computer from potential intruders, because no matter how "password protected" your system seemed, just inserting a floppy, was able to circumvent that. Now, that need not happen. Surely, you could think of "letting access, if moderated" but if the moderator is yourself (& what better sage were you thinking of depending on more?), then I should remind you that, any instance of forgetfulness, could hurt. That is, you may simply click "yes" as the moderator (& enetering your password), but then you may notice that the disk you had inserted was the wrong disk (or, microSD), maybe that of your classmate sitting next to you, or your other disks (or, microSD cards). So, the risk is a bit more, that way, as compared to having external pairs, by themselves.
If tablet-manufacturers would just market such a tablet, then, I may add to the list a small plug-mate module for regular work. That is, unlike when you are re-writing your OpSys at the slot2 (dataSlot) and installing into slot1 (opsysSlot), which may rarely happen. Almost always, you would like to have the two microSD cards travel as a pair, and therefore, a plug-mate may hold both of them. That is, if you insert not individual microSD cards separately, but within that two-slot-unit, to eliminate the risks completely (presuming that nobody hacks the internal of your tablet, but even then, if there is no internal storage, then all they would attempt would be extravaganza like installing/soldering some new chip into your tablet).
No need to load any extra (or, underlying) virtualizer system, either. Just the machine itself, as in the good old days.