Not what I'd do with the Pixie. I'd market it as the affordable and robust counterpart. Keep it on the 270 standard engine to keep prices down and make it available earlier in the up-teching process. XLFE are stage three.
You can fit endo and ferro just fine. The Pixie is only using 17 optional crits. Endo and Ferro each need 14. The cockpit stuff, engine, gyro, and mandatory actuators add 27. That's 72 crits out of 78. If you go to one point shy of max armor you have 1.5 tons left.
If Endo and Ferro are available before DHS you can limit yourself to 8 tons of FFA, which is still equivalent to adding a ton of standard armor to the PXH-1, trade the machineguns for flamers, and add two heatsinks, though I think they're being very silly worrying about infantry ambushes on something that can jump 6. The only infantry it can't easily get away from are motorized and take more damage from non-burst weapons anyways. I'd add four heatsinks in place of the machineguns so you have the option of ER-ing the large laser if ERLL production comes online before DHS production.
If DHS are available you can ER any of the lasers on the base heastinks and replace the MGs with SRM-2s and CASE the ammo. If flamers are acceptable, infernos do the same thing at longer range.
It fills the same role as the Phoenix at a lower cost. It has a bit less armor, but isn't prone to side torso kills. Even the Lyran budget isn't going provide as many 300+ rated XLFEs as the LCAF needs fast mediums.
Good point about Pixie upgrades, CMW might be smart to do upgrade kits too.
PXH Product Improvement Kit:
mk1: FF armor
mk2: FF armor & DHS
mk3: FF armor , DHS. & ER LL/ flamer
Pixie is a common mech across BT, CMW could do the same thing for all the common Steiner mechs and have Lyran logistics by up everything that CMW can get out the door.
Same goes for CAC and CAC can add the T&T / helmet combo to the mix. Plus CAC can do the same for ASF or at least the ASF they know.
Edit: This idea of upgrade kits may even help the companies that are late to market. Need all the feeder lines for components before you can make a losttech mech.
Kits bring in income and add to the Lyran's defense while the company's R&D, prototype, test, redesign, field test, and build lines for production of end unit, ( to include training of workforce to produce an efficient/ experienced team of workers).
All the above can be done in series or accept risk to have multiple parts of development moving forward at the simultaneously. The Save time or Save money balancing act. All the notes added to the CAC datacore should help greatly with both time and money.
Doing upgrade kits also allows for ensuring parts production lines are able to produce quality parts at needed levels before mech production starts, ( CAC gauss rifle line).