Mines are a good thing.  Most games don't have them; no game does them properly.  Entrenchment gets close, but for two issues.

Firstly, each mine shows up in the tree as a separate ship, which is ridiculous.  It renders the tree near useless once you've dropped a few hundred mines.  Even if they were a) stackable by different amounts (I'd say 50) and in a slightly different 'mine' colour would allow people to track what's a mine and what's a ship.

Secondly, the minelayers aren't automated enough.  Being able to queue mine 'points' is great, but they need an autocast function to replace mines lost to prevent the absurd micro of replacing a minefield every time a single trade ship flies in.  Once you drop mines, the game knows the volume they occupy - if the minelayers would auto-cast minelaying within this volume, a nice dense minefield could be maintained without eight million clicks.

Entrenchment is about digging in; the starbases being able to move removes much of the suck of static defenses at a stroke.  Mines are powerful and hilarious, but they require too much player focus, espcially considering they're triggered so easily.  It'd be a big decision to turn it on of course, because of the cost, but for people like me who are fond of dropping hundreds of mines in a jump zone, but who don't want to constantly check and re-check every 5 minutes to re-lay the minelayers.

Additionally, it'd be nice of the minefield-maintenance would allow the minelayer to be in an adacent system rather than exposing itself to battle; indeed, you could propose a 'mine factory' that would work like the resource factory, sending 'mini minelayers' to adjacent systems to drop new mines as old ones are exploded.