Without getting too off topic,
I work with plenty of EE's and SWE's in my daily business. I think you might be just missing the component of the industry and what the equipment actually is and sold as, which would be a security system panel. The industry and market are always going to be conservative and especially on an embedded platform, not going to jump quickly into the bleeding edge. The industry can't because of UL and related, required listings.
What part of your complaint of wanting a complete package takes away the difference between an M1 and an OPII. The M1 is modular and items can be purchased as needed or desired, where to get the same basic level of functionality out of an OP, you need to buy the flagship product (at 3X the cost upfront) and are limited on serial port location vs. the M1's option anywhere along the bus. The manufacturer would be shooting themselves in the foot in the marketplace if they put a product out that forced everyone to buy the entire expansion or capabilities up front.
Think about it. I can buy a M1, very capable, for sub-$500. The OP is 3X that. Say I don't need the 5 the OP has. There's $75-100 each on the sticker right there. Same goes with ethernet. While it'd be great if every panel out there had a TCP programming or web connection, that's a $100 line item right there on the panel itself. So basically, I already ran up roughly $600 worth of "trade" cost on the panel itself to match the OP on those single line items. Say you want a 3rd party support for X powerline protocol....now you're adding the line item pricing for that on top of it.
The long term solution would be yes, a redesign or upgrade, but it would need to be tempered with reality. Even something as trivial as a $2 on board relay is going to add expense that is passed down to the end integrator and further down to the end user. If you can't justify it needs to be there for every install, it's pricing your product out of the market for another competitive unit.