Ray,
No need for more manufacturers. Vitol Aviation was asked the following question by the FAA: "If the FAA were to accelerate the current 2030 termination date for 100LL, would Vitol Aviation be able to supply all of the replacement fuel for the total volume of 100LL sold in the U.S. ?
The response was, “. . . yes, all of country.”
Keep in mind, Vitol’s pricing model is identical to the pricing model for the whole sale price of 100LL (typically - - for the Gulf Coast region, as an example, 100LL is wholesale priced at the price of Premium Gulf Coast Unleaded Car Gas + $1.00/gallon) The pricing model for G100UL avgas is the same, except the markup is higher, but only because the cost of the raw materials is higher.
Of course, if other producers want to produce G100UL avgas, and they are fully qualified, then GAMI will also license them to produce G100UL Avgas.