I heard they were both discontinued at the same time due to the lack of T17 sized glass tubing. I suppose if production restarted it would be the drop in T12 versions instead simply due to the fact that parts to easier to make/get.
Philips used to make a
F90T12 that replaced F90T17 before they discontinued it. And VHO T12 lamps which might be still made can be used to replace PG17 (although not as cool looking),
