Of all the expansions Sins of a Solar Empire has received over the years, Entrenchment is probably the most respected. It identified a major problem with the base game, the pitiful lack of defensive structures, and fixed the problem by adding starbases, mines, and upgraded structures, all for a reasonable $10. Compared to Diplomacy and even Rebellion, it was far more successful in achieving its stated goals with relatively few issues. However, over the years experience has shown a handful of problems with the system, in many cases compounded by content released after that.
Mines were one of the most requested features for Entrenchment, but in practice they probably were the most marginalized feature. While they could inflict serious damage to fleets, there main effect was to make an already slow game slower against the AI since they were a pain to clear, while in more mobile competitive games they were a waste of resources, and even if they did their job they were to micro intensive to manually replace them. This was made worse in Rebellion, now that scouts reveal mines passively, they no longer automatically target them. In addition, some theorized the vast numbers of mines that could be built in the game could contribute to late game lag.
To try and resolve these problem, mines have been totally reworked. They no longer directly explode against their targets. Instead, each mine simply represents an auto renewing mine field, and will passively damage and debuff all targets in the minefield overtime, instead of exploding all at once. The range of each mine is substantial enough that only a few are needed to cover the same amount of space hundreds of mines did, so each gravity well can now only have 10-20 mines each, instead of 150+, which could improve game performance.
Scouts clearing mines have also been reworked. Now that there are far fewer mines, its viable to have them target a single mine again. And instead of simply revealing mines to enemy targets, the scouts will automatically destroy the mines after 20 seconds, so they no longer need additional support units to help them sweep. That said, the mine sweeping can be aborted if the scout takes too much damage, so defending turrets and starbases will need to be dealt or distracted by other forces if possible.
While Starbases themselves will not be changed much in the next version of Enhanced 4X, their counters will. Intended to deal with the powerful defenses they just added, antistructure cruisers have suffered greatly from the different races having huge differences in their quality (or not having one at all), and the fact most players found it easier to deal with them by building tons of bombers, the counter to structures in the original Sins, which can also be used to destroy regular units. In fact bomber spam is probably the greatest imbalance in the game, once you have enough of them its extremely difficult to counter, very mobile, and it lags the game far more than any other strategy.
To try and encourage players to use antistructure cruisers, bombers now deal 25% less absolute damage to structures and starbases. Antistructure cruisers have meanwhile been buffed with additional effects that can be applied to their targets, like Ogrovs preventing passive regeneration for a brief time. The other races' cruisers will also be reworked to try and be more useful, and the Vasari will receive a unique but mass produceable antistructure unit that they currently lack. Starbase abilities like Meteor storm will also be revised so that antistructure cruisers can attack them without fear of being destroyed. You'll need to use other defenses, like hangars and mines, if you want to protect your starbases from these threats.
In addition to bombers no longer being as effective to structures, many other changes to strikecraft will made in the next version. According to the developers, strikecraft are the main cause of late game lag. To try and deal with this, strikecraft will be buffed by a modest amount, but carrier cruiser fleet supply and costs will also be increased. This should mean a fewer amount of squadrons can do the same job that many used to do, for the same costs and fleet supply. In addition, TEC and Advent squads have had the number of fighters per squad reduced, but the stats of each fighter increased so that the total squad's stats are the same, which should further help this issue. Visually this will won't be hugely noticeable, but it should result in far fewer fighters flying around in swarms late game, and could lead to a serious improvement to performance.
Any comments and concerns are welcome, and many things are subject to change depending on how these balance changes play out.