In the Summoning, you could carry bags and such in your main inventory. This was because the main inventory was rather limited in size.

To put something in the bag, you simply drag and drop it in there. To get it back out, the character had to hold the bag in his/her hand, and root around for whatever it was.

Only the first shelf of the inventory was visible on the main play screen, and you had to drag the inventory screen up to see the rest. This while the game continued running along behind it. So you had to be fast to swap out weapons, or grab a fresh one of your old one broke, while in combat.

This was in an old real time RPG, from around '92. Veil of Darkness had the same engine, and the same system, as well.

Not perfect, but it forced the players to make sure they were safe before digging around.

I think you have the right idea with the animation thing. I wouldn't stop them accessing the inventory if they're distracted during that animation, but I would have them vulnerable during that period.

Once the inventory screen is up, they have as long as they like to switch items around, and equip what they want. But when they exit the inventory screen, you can then play another animation to represent them unequipping old items and equipping new items, leaving them vulnerable for a little longer, with duration proportional to the amount of items they have moved, equipped, or unequipped. This represents the fact that they would still be vulnerable while shifting things from one hand to the other and rummaging through a bag, but it also allows the player time to think about this and to be tactical about their selection. They could presumably also click a cancel button to leave the screen and incur no significant penalty.

That's a great idea.

I don't think a delay on the entrance animation will be necessary. The first one could be extremely quick, such as just kneeling down and grabbing something from behind. The inventory would then open, allowing them to decide how much time the exit animation will take by swapping more or less items. It allows unlimited thinking time, while still accounting for the number of real actions that were taken. Having our cake and eating it too.

On the other hand, if being wounded doesn't cancel the actions, but still cancels the animation, the vulnerability isn't as enforced as I would like. Typically, the player doesn't have to worry about one or two hits (he regenerates), so it might be reasonable to do this right in the middle of chaos.

It may be possible to make different animated segments of general actions for swapping equipment. When attacked, the current short segment restarts. The player could either be willing to continue to let them play out, hoping he won't be hit again, or cancel the rest of the animations by taking action. Seems annoying, but I'm not sure what else can be done.