My take on this is that the firms wanting to keep up have two choices:
(and their best bet might be to choose both)
1. Hire up the best interactive talent possible as fast as possible, while keeping in mind that the best talent might actually be current client-side folks.
2. Acquire (or merge with) a top-notch interactive agency and hope like hell the cultures fit. Two greats apart might equal a mediocre once together.