I'm guessing that would be a straightforward repair for any builder doing ti. Fietsbob suggests filing a "V". I was thinking a clean hacksaw cut. This stay-end is a bullet plug that inserts into the chainstay. There's plenty of material there. If the crack continues, the dropout would be free to move back (limited by the "spring" of the seatstay) but not move vertically or side-to-side until the bullet has slipped fully out of the chainstay. (I'm guessing there is a 1/2" of plug or more in there.)

Edit: Clifford,. I highly doubt anything catastrophic will happen. I've broken chainstays behind the support while riding and just noticed a small difference in feel until I looked down and saw the chainstay swinging a little. Rode home with no issues. (Granted a flat 2 miles.) Bikes have a lot of redundancy in that area. The left side alone is enough to keep things together. Then you have the hub and right seatstay. So all the OP needs to do to avoid the worst is to be a little attentive. Feel an change? Look down before diving into a corner and doing a hard sprint out.

Ben