If there is the possiblity that the weight of your gear will make you drown, when its not necessary anymore to display a weight/max-weight status. Imagine that all above the max-weight you can carry is the point at that you would drown, but as you cant carry more than that max-weight, you cant.

Well, I've never swum with full military gear nor have I ever worn full military gear, but I imagine it must be quite heavy, especially in the water. So I must disagree that the weight bar would become redundant, as I imagine you becoming 'too heavy' happens quite fast. The point of the ticket is that IRL, it would cost energy to stay surfaced and you would eventually become fatigued and drown, this isn't currently simulated in any ARMA game at all.

there should be a marker somewhere on the encumbrance level that tells you whether you can are going to float or sink

Also, inventory should be accessible in swimming mode, so you can quickly shed off gear. Soldiers do this in real-life with body armor when swimming.

When Soldiers have to SWIMM to a mission point, the should put there stuff in plastic bags.

In Reality the use there raincoats and make a big bundle with all the gear that floats. this "little raft" gets the weapon on top and the swimmer is pushing it.

Very easy. B U T - takes some time for preparations!

By the way: Archimedes say: "not the weight itself is important for floating." It's the overall density.

So it is very realistic that You can still swim with a gear - to heavy to lift it up on land. But of course it would need a lot of extra boyancy!

And this makes a swimmer slow and clumpsy. And vulnarable to CURRENTS - like in fast rivers or on a rocky shore...