I liked wire fields (but not instead classic wire) and I would like to had more possible choices (slowing down enemy units instead blocking) for sappers (CE,pios), also wire fields would be great if light vehicles could drive over them without crushing it

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Wire field placed on enemy retreat path would be devastating.
German minefields would be great as well If you could put fake minefield signs to tease opponent, Yet i think that S-mines would be much more useful as separate tile (instead 4 of them).
Sappers sandbags or trenches(similar to shell craters, not British-style trenches) would be great addition to infantry warfare, for now infantry is often very exposed in late game and being able to dig in would be very useful.
EDIT_1:
I don't think that tank traps are necessary, they was mostly used to block choke points anyway