Trojan scanners definitely have a future as most virus scanners are behind in both detection and removal of trojans. Consider what a virus scanner will do if it does find a trojan on a system: It will alert the user and block file access. Most users will have no clue how to proceed from here. Trojan scanners, of course, specialize in trojans and malware that is running on a system and will be able to deal with them in a way that virus scanners can't at the moment. I also know of no virus scanner that performs registry, memory and port scans like TrojanHunter does. This of course means less opportunity to detect trojans by the traces they leave in the registry and elsewhere.