"Relevance" is a completely subjective concept.
Personally i like the look of the guitar, regardless of who's name is on it. I also happen to be a fan of Billy Corgan's musical output, but that has nothing to do with me liking the guitar or not. I often hear and see people lumping Smashing Pumpkins and Billy Corgan as an artist into the "grunge" genre. To be fair, for people who actually know any real detail about the man they would know that this categorization is completely incorrect. Take a listen to any of his side projects or even any material released by him in the last 10-15 years. Not "grunge" at all. A better description of Pumpkins music would be alternative rock. His musical output spans the gamut from shoegaze to electronica. He is influenced by everything from Bauhaus to Black Sabbath.
In terms of Reverend having a signature Billy Corgan guitar being a commercially smart decision or not, well lets look at some of the facts:
He has been constantly active as an artist since 1987
He is a respected poet and author
He owns the National Wrestling Alliance
He has produced many chart topping bands as well as award winning movie soundtracks
He has collaborated with, influenced and performed with more famous and respected artists than you can shake a stick at
He was a close friend with David Bowie who openly respected and admired his talents as a song writer\
Even taking one album into account, Mellon Collie and the Infinite Sadness sold over 20 million copies in the US alone
World renowned producers such as Alan Moulder, Butch Vig and Rick Rubin have referred to him as a musical visionary and perfectionist
He has written more instantly recognizable melodic hooks than any of his contemporary's (think hooks in 1979, Today, Disarm, Cherub Rock etc.)
His social media presence both personally and as the Smashing Pumpkins has a VERY healthy and active member base
He owns and operates Madame Zuzu's Tea and Art house in Chicago
Is a respected and revered member of his community in Chicago with the "keys to the city"
His interviews on channels such as Alex Jones rank as some of the most viewed
blah blah blah
I am not surprised he and Reverend are working together. He did after all use their guitars years ago during his Future Embrace solo period, well before they were a "mainstream" brand.
More importantly, the Reverend signature has been extremely popular by all accounts and is sold out through most distribution channels.