It´s quiet rare that i reply on a thread, but since it´s a very important topic for me, i will share my thoughts about it.
I like the idea of "silhouette-mines" seen on every door with like 3 mines/door. And that those mines can be purchased by every char for a "fair amount" of credits. So i was thinking of the following:
"silhouette-mines" can be seen on the floor with a slowly flickering contour to indicate, if the mine is placed or need to be placed. (flickering = no mine is placed, like you experience in other games, where you can see the "ghost" contour of your object and if it is placeable or not)
we need a simple user-friendly system to know how to place/replace mines in a building. Instead of using a cabinet i would prefer something else. I would suggest to "press and hold E" for like 1-2s per mine to "place" those mines. we can still use the mining animation, since it´s the same task. A simple and short info message will pop up, when you are in range (around 1-3m) for example >>> "press and hold !keybind! to place mine" <<< It should be in the same category like when you get close to the purchase terminal. To avoid interacting with the PT instead with mines, the delay of 1-2s is added and the range is restricted to a close area around the mining zone.
to avoid "to dynamic changes per map-typ (flying/non-flying)/building" a mine should cost around 50 credits. It sounds pretty expensive, specialy at the start, BUT in compensate you will get 1VP(maybe 2VP) for every mine that is placed by the player. So "base-deff-player" have a higher chance to gain VP just by "maintaning" the base. And if people realise, that you get VP for replacing base mines in a building, the effort to replace those mines will be higher, since it´s some psychologically point of view too. If you can get something without much effort, people will do it.
Something about team/personal - mines:
I wouldn´t suggest to make mines a purchaseable item, it will cause to much problems with balancing, like buyable EMPs or carbines for hottys/techs, we have seen in the past.
Instead every "buyable-"char should be "unique" it it´s own way. AT- inf have mines, AP-inf have nades or mines. So i would suggest to remove the mines from hotty/techs in the weaponslot and place it in the "X-slot" like patch and every other char who use nades. So only hotty/techs are able to "tactically" place mines, for deffending or even for attacking and covering ion/nuke beacons in a rush. MAX personal mine limit should be 3 (like mines for a door).
I agree on the team-mine display on the HUD. It sounds "fair" for a sneaker to "only" disarm 3 mines while there is a team mine counter + base deff player who will get a bounty for replacing disarmed mines, so even more people will take care of mines (in theory). And also some "unpredictable" mines from deff-player running around in the base.
Also i just want to remember everyone about something you hear sometimes in matches. People complain "how did we lost X-building?" Even the best base deffend like laser fence/mines/turrets will be useless when the team isn´t reacting to any team important infos like rushs/spies/mines/sbhs. So a mining "re-design" will help but not erase the chance to lose a builing in only 30s.