Looks like I lost myself a little in this revision.
Siege Scouts should be priced at 200 points (maybe 225 if I get negative feedback). As for their name, not a problem. What's in a name afterall?

Troops are generally cheaper due to lack of transports and the removal of their 'potential' to act as Air assault units. If you take Drop Pods, you will find that you pay standard Codex prices or more! Hence I feel it is balanced in this respect.
Castellans can shoot with or without IC. Adding them to a formation was a cheaper solution. It is no different to 8 Whirlwinds, except this formation in the list can choose to fire 4BP IC instead. It was a solution so as not to introduce too many new units at the start without a playtest. Castellans are more expensive, so I am open to making the an upgrade to Whirlwinds.
Hunter Upgrade was 2 just to make them different. As a defending force, I see no real issue with them having 2 if they are prepared to spend the points. Notice that if they do want them on the move, INF are going to have to buy transports - not a cheap proposition. Also it opens the formation up to AT weaponry. I think people need to look at the list as a whole rather than its individual parts. If you buy them as part of the Armour, then it makes me happy that someone is considering this formation at all.
Tarrantulas to INF - why restrict AT weaponry to hit them? As they have no crew, does it make sense?
Hyperios Formation - It is yet another option to take in the list. It was an idea from feedback and I think it should stay until playtests advise otherwise - just my view however.
Siege Titans - I want to have the list played with as much standard as possible at this point before we go down that path. It is always an option, and if there is enough push, no doubt it is an easy replacement.