I have one primary wish and that the science advance depends on your play style, for instance if you are warmongering then next revelation is in that sector. Your option to choose may be in this war sector very high (beacons used to reveal are consequently lower). If you decide to reveal some pacifist knowledge, beacons charge will be a lot higher). I would implemented the rule that in start of each era you decide your ministers (for instance you will have 1-5 point war mongering minister, if decide 1 then you war efforts will be minimal in that era - off course you could change him but revolution would be possible and with that unhappiness).
There needs to be a LOT more interaction between Playstyle, or In-Game Activities, and Tech, Social and Religious Policies. For instance:
.....How can you choose, and keep active, a bunch of 'Honor' Social Policies if you never fight a war?
.....How expensive will it be to research Sailing if your first three cities are all in the middle of a Pangaea continent?
and, conversely:
....How expensive will it be to research Sailing once you see someone else's Cargo Ship or Galley go sailing by on your coast?
ALL Techs should have a 'diffusion index' to indicate how easy it is for them to spread: see a Wheel in use, start making and using Wheels: real easy to copy that one. On the other hand, see a Musket... hummm ... you need to know how to forge metal, make gunpowder - not so easy to copy unless you have all or most of the Required Technologies.
And, as the technologies get more complicated, the copying gets harder and the numbers of Required Technologies and industrial plant get more difficult: see a computerized solid-state personal cell phone, and it might as well be a Magic Wand if you don't already have some understanding of Electronics, Solid-State Circuitry, Computers, and access to or the ability to build Satellites or Communications Towers. Oh, and don't forget advanced metal-working, Rare Earth mining (for the solid0state components), and basic electricity, digital communications, etc etc.
In other words, Very Hard to copy or pick up.
And some Technologies may be copyable, but their application may be beyond you: see a Kalashnikov assault rifle, and a village blacksmith may be able to copy it, but your nation may not have the ability or resources to build the factory complexes required to manufacture them in quantities required to equip an army. Even if you know steel-making, armor plate, big guns, steam propulsion, et al, you may not have the massive industrial ship-building base required to build Battleships (historically, only about 7 countries in the Entire World were able to build them before they became obsolete!)
The speed with which you access Technologies should be variable, dependent on your surroundings (What price Irrigation to cities in the Desert?), your activities (Trade partners, war, peace, large empty lands to settle...) and even your Social Policies should interact with how fast certain technologies are available.
Likewise, ALL technologies are subject to 'spread'. Some faster than others (see above), but between the increasing complexity of the technologies (Bow versus Musket versus Railroad versus Atomic Bomb?) and the increasing speed of information diffusion (writing, printing press, telegraph, internet, etc.), there is nothing that cannot eventually be 'discovered' from your neighbors and copied with varying degrees of difficulty.
Adding this to Civ VI would solve several problems: runaway technological superiority, nations adjacent to each other at wildly differing Era-levels, and dull End Game where you already have such a superiority in tech and getting to Wonders and Projects first that the game becomes dull. All real problems now in Civ V.