Titel says it all 
My Wish Is, to make Meinwerk more useful and enables HRE a better and longer feudal age.
An Idea :
Make Meinwerk Discount a bit less, but also unlock the Castle age infantry techs (or some of them) .
Maybe make Aachen also abbit mire expencive (450,220)
I wait for your ideas
i would like to see MW buffed, but HRE are already pretty flexible, so even though HRE is my fav civ, i think it will have a larger impact on the game if we see things like abbey of uselessness, chamber of memes, kremlin of junk, or tower of defeat (albeit delhi itself needs a retune) buffed first. since the meinwerk sometimes has some viability as opposed to this list of unused stuff.
maybe kremlin first since rus in such a bad spot?
Ill just go in alphabetical order:
Abbasid: Military wing could be less camel focused. Maybe have boot camp give +20 flat hp for a bigger early boost for agression that falls off later. Abba could use some diversification for openers. House of wisdom can train imams as soon as you get the culture wing - make them relics feasible for Abbasid.
Chinese: Eh, things are fine.
Delhi: Rebuild everything. Everything. I have ideas, but for now any change to the Hisar Academy is a gain.
English: Abbey of Kings acts like a monastery - but cant train monks till at least age 2.
French: Chamber of Commerce provides its trade income boost to all markets instead of only to itself. Maybe gatekeep it behind a tech for easier balance tweaking.
HRE: Add in the description “This civs is has access to ranged infantry too.” to every landmark description. In all caps.
Mongols: They have the best landmarks and need them as is.
Malians: Swap Farimba garrison and Mansa Quarry.
Ottomans: Sultanhani Trade Network - same thing I said for Chamber of commerce. Istanbul Imperial Observatory also gives a 30% cost reduction for techs researched in it.
Rus: Golden Gate recharge rate scales with number of active traders to a cap - smth like a maximum of every 30 sec at 20 active traders. Kremlin has more garrison space and more line of sight. High trade house trains deer on demand for a smaller food cost.
I think it would be a good strategy to make blacksmith armor and attack upgrades available 1 age earlier or even all of them in age 2, like french Royal Institute has age 4 techs. (It is an age 3 landmark, so it is not the same, but you get the idea.) Maybe cost reduction would need to be adjusted. It is also not clear to me what makes some upgrades available in blacksmith and others in military production buildings.