RichDirt is for sure a VERY cool tool. I have used it with MR for 1-2 years and it can really give things a push towards realism.
I am frequently in contact with Matthias from EnrichPro - the producer of RichDirt. I have been trying to convince him that Corona should be his next move. I caught him probably at a very bad time, as it was at the time Vray 3 was about to release - and he was struggling to get an update ready for this.
Matthias is a little worried about if he will earn enough porting Richdirt to Corona. There are many render engines out there, and its always a little lottery to pick the next to port to, - and see if the programming effort gets payed off. I really try to convince him that Corona is a sure and safe pick for next porting - especially for the archviz world - which, I guess, may be seen as his main customers.
I don't know how much work there is in porting RichDirt to Corona - but I would for sure recommend Ondra to contact Matthias for a chat about a common effort in getting RichDirt working with Corona. I am sure a push from other users of Corona would make the decision easier. So please go in at
http://www.enrichpro.com/en/richdirt/contact.html and give Matthias a push towards the light :o)