Multiple adrenaline shots, perhaps adding up to a slightly shorter time, would be a nice change. They would allow the VIP to escape from guards without then having an extra 5 seconds of super speed left over. Whenever i was forced to use it, i would almost always go straight for the other VIP if he was close as it just felt like a waste otherwise.
One other thing I've always found a bit lackluster about this mode is the tendency for it to be decided right at the start. The braver/luckier/tougher VIP will usually end up getting his team either RCP90's or lasers pretty quickly, as the shotgun easily beats out the DD44/PP7. This then makes it near impossible for the enemy VIP to get his team an arsenal that competes, since the shotgun is mostly outclassed by the higher level weapons. The match will usually go on for a few more minutes, but the outcome is pretty much decided once the first VIP goes down. I think this mechanic worked well with the old system, where there was just one VIP, as it prevented things from getting too campy as a VIP that did nothing would soon get chewed up by P90 spam. However, with multiple VIPs i think the that the advantage is a bit too persistent.
Perhaps have a team's weapons drop a few levels or reset when they successfully kill a VIP. This would still encourage VIPs to expose themselves and be proactive, as leveling up your team's arsenal would be a constant responsibility, rather than something you do at the start that lets you hide behind a wall of P90 spammers. It would also help the loosing team regain ground, as their next VIP would have a much easier time defending himself and his team might have a weapon advantage over the enemy if the previous VIP got anything done.
This should be pretty easy to code up, so it's worth some testing if nothing else. Can't wait for the new version!