I think the series might be done with zombies proper, which suits me fine. Always with the damn zombies. Based on the events of RE1-4, Umbrella Chronicles, and Regeneration (which is canon), and the brief BOW's in the demo, I think this is what's going to happen in RE5:
Wesker already has the T-Virus. Despite its failure to create truly intelligent BOW's, the T-Virus allows its hosts to be more genetically stable. The Nemesis was created with the G-Virus, and although it was fairly intelligent and took orders, it mutated at every turn and eventually became totally unhinged. Thus, Tyrants created with the G-Virus are not really an option. The most stable Tyrants have been the Ivan models, which were modified Super Tyrants. Wesker also discovered the G-Virus thanks to the experiments on Lisa Trevor.
Anyway, Wesker missed out on the Code Veronica virus because Chris and Claire went and killed its sole host (and the corpse went up in flames). At the end of RE4, Wesker got ahold of a Las Plagas sample.
At the end of Umbrella Chronicles, Wesker stole all of the data from Umbrella's Russian branch, where the best Tyrants were produced, including the Ivans and TALOS. TALOS is unique in that it combines the strength and genetic stability of a standard Tyrant with remote behavioral control. The TALOS model is essentially a puppet, even after it mutates into its final form.
The BOW's in the RE5 demo have wings and increased resistance to gunfire, which strongly implies that they are "infected" with the T-Virus. Because humans have proven to be such unstable or unsuitable hosts for the T-Virus (for military purposes) and the G-Virus (for stability purposes), I'm guessing that the next step is to create more powerful Plagas.
Just a thought!