4. What else?
It is possible that in the future, workarounds similar to that used with Active Directory may be required for other protocols. Workarounds for multiple protocols may be mutually incompatible and we are required to choose which, if any, will be implemented. We would much prefer to avoid this situation.
It is also possible that at some stage in the future, http ceases to be the "dominant" protocol in the eyes of the average user and there is a call for an A record to be used for some other purpose. If this seems far-fetched today, consider that originally A records were often used to denote mail servers (prior to the introduction of the MX record), and that in the 90s it was not uncommon for a department to want an A record for its domain name to point to its login gateway.
In the case of unit.ox.ac.uk, we can in principle support an A record for unit.ox.ac.uk for one particular service, with the clear caveat that this may cause them problems with other services in the future. If such problems arise, it is then up to the unit to decide how to proceed.
In the case of the ox.ac.uk domain, multiple teams in different sections of the University are responsible for different services (eg OUCS, ICT support team, UAS, BSP), greatly complicating resolution should any conflict arise.