Part of the issue is licensing. Because Red Dead Redemption 2 is trademarked by R* in multiple jurisdictions, I imagine it's variants are as well.
Let's see...
http://tmsearch.uspto.gov/bin/gate.exe?f=doc&state=4806:3u2zdt.10.54
That's Take Two Interactive's filing for Red Dead Redemption, including tee shirts. Now, with how Corporation friendly US law is, I suspect that if TTI wanted to challenge the use of RDR2.org, they'd be successful. Copyright claims, especially related to IPs are very protective and have a lot of safeguards against derivative is similar sounding names.
Which isn't to say that it can't be done, but it may behoove anyone considering something similar to entertain only attempting to profit off of original content, like user posts or art (much of which is protected by fair use).