What's that? Sounds a lot like you are admitting that you
can't solve
this problem, or
this. or
these, or
this.
Second link makes no mention of any specific problem
Fourth link is just saying it is too easy.
Interestingly enough, the OP of that thread is making the claim that this tactical module does exist, and is arguing that adding the optional rules into 5e makes it more tactical.
So, I've only read up to the 8th post (and your links) and identified what I think the problems are.
1) Flanking is too powerful
2) Flanking is too easy because of new Attack of Opportunity rules
So, before I read any further, some suggested fixes.
For #1, I have a DM who didn't like the permanent advantage because we had a large number of NPCs in our party. So instead, we use this rule. (Not written in rule format, because we did this verbally at the table and didn't bother to write it down)
Flanking-> When flanking an opponent with an ally, you gain a +1 to the attack roll for every ally you are flanking with (ie, if you have 1 ally, +1, 3 allies +3). This bonus maxes out at your proficiency modifier.
You could also just make it a flat +1 (I think +2 would be a little more impactful than some people want it to be, due to 5e's bounded accuracy)
For #2, I would say the easy solution would be to institute the old AO rules, since that seems to be the issue involved. So something like
Attacks of Opportunity-> If a creature moves 5 ft while within your threatened range, then you can use your reaction to make an attack of opportunity, unless they have taken the disengage action before moving.
You could even add in that making a ranged attack or casting a spell triggers attacks of opportunity as well. But I think that would be going too far personally.
That took me... well, I read some other threads first, so we'll say 10 minutes since my previous post currently says it was 15 minutes.
Edit: Ah, now that I got to your personal post (I wanted to read up to it) I see that you want to make things incredibly difficult.
Towards inventory... I wouldn't bother with a rule for it personally. 95% of the time, no one bothers grabbing an item from their inventory when combat starts. You could also add in that AO happen when you take the Use Item feature. If you want to give some creatures the ability to cast spells without triggering AOs... I guess do so? It shouldn't be that hard, but I'd have a bear of a time trying to remember who I gave immunity to casting AOs to and who I didn't. I'd probably just make it a blanket "casting spells" if I truly wanted to go that direction.
But frankly, it sounds like you just want to take all of the abilities and rules of 3.5 and port them exactly over to 5e.
That's called playing 3.5. Just do that instead of making every rule in 5e match 3.5.
/EDIT
But, I should read the entire thread, make sure I can find anything else, especially since I haven't seen much about facing yet.
Ah, seems that I found the post you quoted, so I should address those points.
- Weapon rules, well I'd suggest looking on DMs Guild, weapons are a very common homebrew topic.
- Alternate crits, we did play with a "crit deck" of cards on Roll20 once. Had a lot of effects other than damage, also DMs Guild has lots of homebrew for that. Should be easy to find
- Tripping already exists, all it does is knock prone and that got absorbed into shove
- Sundering is trickier, might have to come with the weapon rules. You could use the DMG list of materials and health. That would give a sword an hp value of 10(3d6) and an AC of 19 to strike. Super rough answer, but I'm doing lightning round edits since I have to respond to an entire thread I wasn't even a part of
- Beefier rules for vertacality? Not sure what that even means. Could just be the diagonal movement rules, which do exist. Moving on
- Hex-based combat? You just use hexes. I have no idea what could possibly need to be written into the game for this. I use a hex map all the time so that radius spells are radi instead of blocks.
- Tactical Mass Combat. I agree, need a good system for that. I'm currently using the rough model provided by Matt Colville in his Strongholds and Follower's book. I'm looking forward to his Kingdoms and Warfare book that is going to provide a much deeper system. That is not something I would homebrew on my own, and it actually a complex subject that goes beyond tactical combat and into an entirely new system of play.
- Expanding Adv/Disadv to encourage stacking? I would just rule they stack. Done
So, read the entire thread. And other than your post demanding that every rule and exception from 3.5 exist in 5e, I think I found some quick and easy solutions. You are sure to tell me that I don't understand anything and that these solutions will clearly never work, but considering some of the them are rules that I am actually using I can say that yes, most of this would work just fine.