AoC: Thanks for your comments, I'll try to address everything and explain the rationale behind it and then see where we stand after that.

1. The Majoris changes were implemented for two reasons. 1. to reduce unit count and allow for more fixed types of Majoris. What you see here is the first step, the next phase is to add in more named versions. 2. the switch to support was to prevent the Majoris access to a CLP Minorus upgrade when using the mars weapons system. This was to alleviate E&C's fears that the combination would be overpowered.
Fluff wise, the majoris is the more rare of the ordinatus with each one being named for the place of origin or the conflict it was built for. This means they shouldn't be as common in the lists as the minorus or the hypaspists and placement in the support section does this although it does still allow for a large number of them to be present if desired. Along those same lines, limiting the majoris to named weapons allows for them to be more thematic rather than simply generic weapons platforms.
2. We did try this to an extent in draft a. Mole Mortars and Rapeirs were implemented as options for the infantry upgrade option along with Praetorians and Secutors. The just didn't receive much attention and were never taken. This was also the issue we had with them as a separate support detachment. The current versions assigns them to the Sagitarii to allow them to boost their numbers.
3. Chimeras are gone for good. Fluff was found that shows the Chimedon was used only by Tech Guard which is why it was substituted. It's basically a chimera with a cannon on top and less room for infantry. I'm also avoiding things like the Gorgon since it takes away from the AdMech flavor. Since we want minorus as a primary focus, using them with a Assault Pod is the way to go for heavy transport.
4. This is a rather more complex issue. I'm not against adding more choices in the infantry upgrades however there are some problems with your suggestions.
Base Formation: check, this is what we have. no surprises there.
Shooting formation: This is effectively what the sagitarii are although to keep with the idea of the multiples of 5 in the list it's 4 sagitarii and one tech priest. We've currently got this as support and they are a pretty versatile formation that I think could easily get out of hand if placed in the Core group although the thought has crossed my mind.
CC formation: This almost happened as 4 secutors. Eventually I decided that it really didn't fit the fluff to do this, especially as a core formation.
Skitarii Support: I'm not opposed to adding back the extra skitarii stands however the sagitarii can never be part of this option.
OK. Infantry fluff this is why some of your suggestions can't be inplemented:
Secutors: they are described as rare units as such allowing access to a stand here or there fits their fluff more than a support formation that could be taken multiple times. Adding limits like 0-1 means they don't scale as points go up which I dislike. That's why they ended up as an upgrade to the skitarii where they would show up sprinkled here and there rather than a large number overall.
Sagitarii: These are specifically described as heavy weapons troops that are NOT part of hypaspist formations. Any heavy weapons in a hypaspist formation are simply called hypaspists; this is why we can't put them in the support upgrade. I have no problems changing the plasma stats. They were originally changed from the default slow firing to the current to match the minervan list. If the stats are changing, I'll change them to match. On mole mortars. I didn't want to remove the option but they just don't seem to be taken as separate formations or upgrades. Giving the Sagitarii the option to swap seemed like a good idea since it gave another heavy weapon to the group and gave them flexibility in their roles and hopefully allow the mortars to get some use.
5. I don't think this is necessary. Both the minorus and Majoris have AA capability with their HB so you don't gain much and doing this would get pricey with the minorus base price. Taking out the hydra negates some peoples collections entirely. As an upgrade option there is at least a place for it with the Flak support detachment removed.
6. I agree with you here. I'm thinking the Defense Laser would make a fun option for the Skitarii list to replace an objective on their side of the table with, but I've not sat down to work on it. I think doing this would allow for a more defensive oriented play style too.
7. Fluff wise I think they need to stay allies. They are listed as fighting with Skitarii although we don't know if they were operated by IG personnel or Skitarii. With the 33% allies you've got a max of 2x detachments in a 3k game which is down from the potential 6x or so detachments if left as support. It also competes with Thunderbolts and titans which pushes it further down the list.
Speaker: IIRC they are just noted as heavily armored and armed with ancient weapons. While it isn't necessarily a problem to disallow transport in chimedons, I kind of like the ability to do so since it gives a mobile formation a nice boost without Minorus transport. I'll note it for future thought though. Lets focus on nailing down robots and sagitarii before we get caught up on tweaking the secutors.
-Let me look it over. Changing it in Skitarii would change it in AMTL since the option is selected from the TL list. I need to see how that would affect things.
-The corvus pod is an actual weapon option not an upgrade so while I guess we could do a specific transport minorus, it causes complications with selecting components. Are you referring to any particular circumstance? It would help to know what the context is with this.