Card Initiative

Here's what I do in my own little games where I use cards:

1 card per unit

No cards for command units (act on their discretion) (or sometimes we insert 3
commander's option cards and the commander can collect them
and then play them at any time to take his turn - but he only gets
one activation). When we allowed this kind of pre-emption, it wasn't
mid-activation. It had to be before or after.

Overwatch/Reaction figure is a pre-emption. Since it is really "last
turns fire" (for Overwatch), the unit's card is still valid when it comes up.
For Reaction Fire, the units activation is consumed, so the card is ignored
when it turns up.

If two units should go at the same time (any situation where a card has come
up and an officer wants to activate someone or reaction fire is desired), we
roll QD vs. Ldr. Whoever beats their Ldr by more goes first. (You could also
do QD vs. QD opposed). This sometimes happens in cascading interrupts.

Case: Red activates (by card draw) unit X. Blue doesn't like that, so Blue
Leader wants to pre-empt. So he rolls off with Red X. If he preempts,
Red Leader may decide he wants to try to pre-empty Blue Leader. So
they roll off. Once a leader tries a preempt, he's activated (can't take it
back) but he can spend his actions however he likes (thus if the order he was
going to give is no longer viable, he can issue another)

This works and is fun. Chaining of events doesn't happen that often.