Here's what I've been saying. Anything you don't like should be ostracized to a mod. A fork of 0A.D. would have to be made. That's going to end up happening.

My preference would a "next" button - just in case you are a bit distracted or it takes a bit longer to read, then you might miss that page. Also, if you introduce a preset timeout, there will be arguments both to reduce it and to increase it depending on whom you ask.  Making that "next" a user decision avoids these discussions.

There are some but for sure, some could be added. I'd love for towers to have a tech for LoS.   I think one game that balance fast units correctly is Total War series. Their games are very much mostly SP, yet, cavalry units (and any fast units in general) aren't nub-friendly. They are high risk, high reward units: In Pharaoh for example, chariots are super expensive but still EASILY one shoted by any cheap spear, jav, and even to lesser extend other missiles units. You can't just rely on having bough a expensive unit to throw into the fray and win fights that way. You need to have the right timing, micro, and combo with other units to make the most out of them. But when you do, the rampage is real. That's what makes a game interesting in my humble opinion. In 0AD Pers and Sele have these champ cav that have for example 2x the HP of a Spartan champ hoplite, with more base armor; and to be a "counter" the infantry has x2.5 bonus damage against them... And that's the best counter there is to them... If ever the spartans can ever reach the cav. You see, it's just obviously bad balance.  

I want to implement a system for unit speech/dialogue in cutscenes next, inspired by that mockup.  Should I add a "next" button (to the bottom right probably) for the player to click through the dialogue themselves? Or always switch to the next line after a set amount of time, like a predefined cutscene? How do other games do it? It would of course be possible to provide both options and leave the choice up to campaign makers. Could that be worth it? Or would one option of those two be always be preferred anyway?

Is there scope for having the javelin thrower as a technology for increasing infantry skirmisher range?

Both @Classic-Burger and @Deicide4u have some good ideas for singleplayer mode. If you want to playtest those ideas, I would recommend you to make a mod for yourself. That is much more efficient than raising suggestions on the forum that will very unlikely be adopted. If you encounter technical challenges, we are happy to help with specific coding difficulties and you can perhaps team up with @Emacz to make his Historical mod better.  Changing anything in the base game will go through heavy scrutiny, especially when tweaking something that can affect the balance, such as your additional techs. Most multiplayers use only the public mods, therefore we have to keep in pristine to prevent game-breaking balancing disasters. If you read the changelog on the gitea, you will see that most balancing changes are very minor increments in stats and something as major as your techs must be tested in many TGs before being implemented. If you don't want to you go through all this hassle to convince the MPs, just do a mod and submit it to mod.io. Hopefully some like-minded players would download it and 1v1 you there.    Back to the topic, I like how it's done in Delenda Est. The techs to take very long to research and some choice to accelerate it would be great. 

There should be chivalric civilizations with broken cavalry. Too broken but not that one class is above the rest. There will be tiers of units. We already know that missile units are support for infantry fights. But it's a shame that the forge technologies don't feel as powerful as they do in other games. RTS are fantasy games of power. Command powerful armies, feel the power of being a general and an urban planner. Armies should feel powerful by upgrading their weapons. There are no technologies for LoS, there are no technologies for repair... There are barely there are technologies for capturing buildings. The nerf thing happens not only in 0 AD, but in many competitive games.