So, one idea I had for an alternate Inner Sphere Battle Armor development path involves Comstar failing to keep the Hurricane PA(L) under wraps, causing PA(L)-scale knock offs to spread throughout the Inner Sphere during the 3040's. After playing with the concept for a few years, the Great Houses decide to produce bigger designs for a direct-combat role, though they'd only be Light BA in size. Anything bigger would be limited to one-offs and suits still under development, though said development is naturally accelerated once the Clans show up.
Design parameters:
Light weight class - Medium and bigger Battle Armor essentially don't exist as far as military planning goes, which makes the Elemental still be a rude shock. They have to expand production for the Lights to hold the line until bigger suits go into production, though the Elemental can still beat them handily one-on-one. It still needs to treat the IS Standard as a legitimate upgrade, after all.
No BA weapons from past 3060 - These are the early days of BA design, so what many would consider "standard" options in later eras don't exist yet.