Well, companies usually keep some sort of cash reserve if they're able to. I don't see any problem with a corporation deciding to keep that reserve in the form of bitcoin instead of USD or some other cash equivalent. Nor do I see any threat to bitcoin's future as a currency by MSTR's actions.
Is it even possible for a corporation to take a decision that would allow them to keep their reserve in any other asset, i do not think so it is possible, if it is a small private firm it might be possible as the individual can take the decision but that is not possible with a corporation as you need the permission of the board members to make those decisions and it is not that easy to convince everyone.
With MicroStrategy one person is holding the Chairman, President and CEO position and hence he can take his decisions about his reserve holdings.