Who are “they”? And how should “they” support it? From point of view of the community - anyone can create a wallet or a client, and if it’s a good software - people will use it. The only two natural problems that arise are:
How do you trust this particular piece of software?
How do you trust the company\person to keep supporting the software?
Most of the people in the community do not have the skill-set to check the code for themselves, or to figure out a lot of stuff that programmers might assume as obvious. And the process of testing, auditing, and verifying a serious piece of software takes a lot of time and resources. Additionally, even if community manages to verify the specific released version of a software - does not guarantee that next updated version will not contain an error, or a serious problem, or an outright hack.
IOHK is not some kind of an overlord, ruling over users. They are hired to develop safe software and to keep updating it in a safe manner, providing as much transparency as possible. So it’s not the IOHK who rules, but the community. And only community decides - will it use non-IOHK software or not.
So when we are talking about “independent” clients\wallets the question should be not “how IOHK support it”, but rather: what does the developer do, in order to minimize required community trust? A good company should itself make sure to show people how exactly they do not have to trust it. People will trust audited software - so hire an audit company. People will trust someone who is active in the community - so prepare people to you contribution, be active in the community, discuss what things may be done differently and why, show people that you know what you are doing. Ask people which audit company they would prefer you to hire. Communicate with the developers to make sure they are interested to verify your code.
TL;DR - the IOHK is NOT “Cardano”. Community IS “Cardano”. So if you’re producing software for the community to use - make sure community will want to use it. They don’t have to ask IOHK’s permission to do so.
P.S. After 2020 community may additionally try to hire IOHK on a separate gig reviewing and auditing someone’s software. But of course, assuming that people would want to spend treasury money on it, and IOHK would want the job.