It is a possibility.
The GS F would compete against the BMW M5, Mercede-Benz E63 AMG, and the Audi S6. It would probably carry a 500 hp V10. I would think it would be priced close it's competition, so around $85,000.
The LS F would compete against the Mercedes-Benz S63 AMG or S65 AMG. It would most likely have either a 500hp V10 or a 600hp V12. Price would depend on who they're gunning for. The S63 competitor would be around $130,000. The S65 competitor would be around $200,000.
If an IS F convertible makes it's way into the Lexus lineup it would go against the BMW M3 convertible and the Audi S5 cabriolet. I would expect it to be around $65,000.
Lexus has said that if a GS F is made, than an LS F is in the cards as well. And when asked about the IS F convertible, Lexus expressed interest and said that based on the success of both the IS F and IS C, an IS F convertible was possible.
Personally, I hope Lexus does come out with more F-performance models.