Key 'problems' of current system are listed in red
Key 'features' of proposal listed in green
[Key Change 1]
Player Mass / Zergs/ Lag - one of the biggest problems in forts has always been lag and capacity. Alot of the intricacies, and what makes fort enjoyable, are eliminated by sheer player mass. Bottom def, 3rd def, lord room def, used to be viable options depending on the circumstances, now it's only lord room. Jail Breaks actually used to have the potential to sway the outcome. Current system, there are usually so many players afk'ing around the jail that a break is very unlikely, and even when it does occur, more often than not the player mass means a successful jail break is insignificant.
Proposed: Reduce fort pop cap and increase level restriction - Reduce the total max number of players in forts. Bring back min level requirement of 40. Use more of the available map space (described below) to allow players of all levels to participate in capturing a fort and get rewards for it. (Pillaged Zone)
A big reason forts are so hard to get exactly right is because everyone, of all levels, want a piece of the fort+invader pie. There is no reason that pie has to be solely restricted to the fort area. Spread players out in interesting ways instead of trying to concentrate so many players in to the small fort zones.
The Pillaged Zone Proposal
[Key Change 2]When a pre-fort zone is locked, open up a previous zone in that pairing in the "Pillaged State". That zone could be one chosen at random from t2,t3, t4, or potentially even tier 1. For example, when 'The Maw' or 'Reikwald' opens up, a previous zone in that pairing is chosen (perhaps at random) and unlocked in the "Pillaged State", that could be either Ostland/Troll Country, maybe even West Praag or Nordland/Norsca.
What is the Pillaged State?
Every zone is divided into a Order PvE Area, Destro PvE Area, and RvR Lake. When a zone is pillaged, the RvR lake shifts from the RvR area, to the PvE area, depending on which realm opened the fort. It could be any other tier zone in the same pairing, but I will use Reikland as an example:
Green Border - Destro PvE area
Red Border - Order PvE are
Blue Borders - Landmarks or Interesting areas
Red Border - Order PvE are
Blue Borders - Landmarks or Interesting areas

Example:
Destro lock Reikland opening up Reikwald. Fort opens, and Reikland (it could be any other zone in the pairing, Reikland for this example) unlocks in the 'Pillaged' state. The RvR Lake, shifts from the center to the Order PvE area (because order 'lost' the zone and destro are are pillaging). PvP commences in this zone as it normally would in any other usual RvR Lake, where all players are flagged for pvp. Within these zones are various Landmarks or interesting places, essentially functioning as BOs for the zone. When these are held by the attackers, provide bonuses to their realm members who are currently trying to capture the fort. For this example specifically:

[1] - Castle Grauenburg
Capturing and holding the Castle Grauenburg strategic point provides the following bonus for attackers and defenders in fort:
ATTACKERS: All postern access points are opened
DEFENDERS: All postern access points are closed or blocked

[2] - Reik River Observatory
Capturing and holding the Obervatory strategic point provides the following bonus for attackers and defenders in fort:
ATTACKERS: provides artillery barrage for attackers (much like the old artillery system forts used to have)
DEFENDERS: provides artillery barrage for defenders

[3] - West Temple
Capturing and holding the West Temple strategic point provides the following bonus for attackers and defenders in fort:
ATTACKERS: 1 BO in the fort remains captured for your realm as long as this strategic point is held
DEFENDERS: 1 BO in the fort remains captured for your realm as long as this strategic point is held

[4] - Raven Landing
Capturing and holding the Raven Landing strategic point provides the following bonus for attackers and defenders in fort:
ATTACKERS: X defenders are teleported to prison
DEFENDERS: opens jail and slightly heals lord HP

[5] - Heinrich Estate
Capturing and holding the Heinrich Estate strategic point provides the following bonus for attackers and defenders in fort:
ATTACKERS: allows more attacking players into fort
DEFENDERS: allows more defending players into fort
Ofcourse these are simple examples and are subject to refinement. Once the fort is either lost or won, zones and rvr lake revert back to normal. Invader medallions should be rewarded to players participating in pillaged zones on an almost equal level to those participating in the fort, perhaps slightly less, or should be rewarded to victorious realm only in order to encourage active participation in pillaged zone. Ofcourse these are details that require refinement.
In this suggestion, with [Key Change 1] + [Key Change 2], forts themselves become less crowded, potentially more enjoyable while still serving their purpose as a gateway to cities. It also provides low rank players the opportunity to have an impact of the outcome of the forts with the potential and incentive of equal rewards for doing so.
But even more, this can in any ways be considered a content patch, but all content already being in place. Reikland might be a bad example, but a very large number of players spend almost no time outside of the usual pvp-rvr lakes, especially in lower tier pve zones. Opening up those pve areas for a limited time in this way, they are untapped battlefields with unmeasured possibilities, and as mentioned, can be considered a 'content patch'
I'm not sure if an endeavor or this scale lay in the realm of possibilities, and would obviously require much fine tuning and discussion