Is it Possible to Convert PhotoShop CC brushes (.abr) for PhotoShop 7 compatibility?

Check out ABRMate - you might need to do some googling, but there's a wayback machine link from Texturemate that worked great for my CS5. New ABR goes in, PS 7 version comes out.

Hi, I am also wondering if offering compatibility with an old, unsupported version if worth the hassle.

But maybe some other third party programs that are compatible do not support the latest version, hence your question?
It looks like they do support most of the options that came circa with the Ps7 brush engine... So in that case it would make sense.

I'd try the tools presets path, as Jeff suggested. but not sure if those would work with third party programs. 

There is also a third party program, ABRviewer that you might want to try.

Bristle Brush Tips were introduced in 2010 according to this article.  That would surely have needed an updated .abr format 

https://www.adobepress.com/articles/article.asp?p=1664592

Then there was the change to the brush engine in 2017, but that was aall about brush management if I am remembering it right, so maybe no need to update the .abr format for that.  We get occasional questions  about CS2 through to CS6, but Photoshop 7 references are very rare.  You'd need and old system and OS to be able install Photoshop 7 as well.  So if it was a mater of maximising the market for your brush sets, would Photoshop 7 compatability make difference?

You can load the Brush presets from photoshop 20/21/22 into photoshop cs4, then save them out as Tool Presets which will open in photoshop 7, then convert the tool presets to brush presets if desired.

It would be very advantageous to have an actual copy of photoshop 7 for testing. Unfortunately, i don't know where to get a no risk permanent legal copy of photoshop 7.

Those won't be directly compatible. You'd be better off just creating the old brushes from scratch. I am also  not aware of where you can download a copy officially.