Well, she's technically still around and available for purchase. Unfortunately, she's not as popular a choice as other V3 artists like Megpoid and Maika, and as the VOCALOID wiki points out, her voice requires some additional editing due to flatness. Also, she was voted the least popular release of her group - ouch. She hasn't been represented in the Nico Nico Douga ratings since her debut in 2011.
I don't expect poor Tone Rion to get a revival movement for her to join the VOCALOID NEO line-up - it doesn't help that so many VOCALOIDs were released after her that have obtained much more popularity - but perhaps we were too quick to dismiss the potential of her soundbank and character. Give Tone Rion another chance, music makers of the world!