I could see these Extra-light Mechs (Inner Sphere Protomechs) being a Mech cockpit (small or regular) with souped-up Battlearmor components rather than down-scaled Mech components.
Similar to how Quad Battlearmor are a cockpit with limbs on the outside, these would be a Mech Cockpit with limbs on the outside. They would use Batteries instead of fusion reactors for power reducing their endurance, but the Batteries can be placed as needed meaning an onboard reactor doesn't cause a cramped cockpit (the Small Cockpit causes a cramped cockpit). Eventually the fusion reactor would be needed for power demands, and you'd convert from XLM to Mech.
For appearances they might be similar to a WH40k Sentinel or the Starship Troopers' Duck.
Most of those suggestions are already adapted. IW.
They use the 'Open Cockpit' concept, basically a motorcycle saddle in a smaller, 1ton cockpit. Its Fireproof, but not waterproof.
Herb gave permission to adapt the Nebula California rules for use with ELMs - that was mentioned in this thread by somebody (I think?) and it was brilliant, saved me from having to create them.
The batteries are a good point - I looked at Fuel Cells, then just decided to use fusion engines to get those 'Invisible' heat sinks. I'll have to earmark it for the next try.
And yes, I have the Sentinel image in mind, too. But.. its not Battletech, and while I feel safe from lawsuits using canon art from Battletech products, but I decided early on to scrap using absolutely perfect images from other sci-fi games and artists online to play it as safe as possible.

Its not the game play I want. Bottom line, I want mechs - not Protos - smaller Mechs. I'm considering a d6 hit chart, one armor column with cut-offs for arms +arm weapons, Leg Destroyed, and some kind of emergency exit 'Abandoned' optional exit - the soldier could stay, but only a short IS bar remains and he's gonna die when it hits '0'.
That's about as far as I've gotten so far. I'm almost done the 3rd revision to the Celestials, just 3 left. Got some major chores to do this weekend, so I doubt I'll be getting anything done again.