In fact its probably likely that diesel race cars will becoming more and more popular , didnt peugeot win the le mans with their HDI FAP , and audi before that in their TDI ... as you mentioned seat have been trialling the TDI in touring cars , and there was even talks of a TDI golf being prepared for rallying a number of years ago ...
If i ever hear a formula one car though with a diesel engine in it , its the day you will find me hanging from the rafters