If you choose not to book OW, what will you then book? How many of the major carriers which provide a relatively large international network are willing to contractually commit to interlining across tickets?

There is no reason for a carrier to do so. All the carrier does is accept liability without benefiting from the revenue associated with single-ticket revenue. Presumably, when booking an itinerary, one books the most cost-effective ticketing scheme. One ticket if all else is equal.

As to protection across tickets, only AA has guaranteed it. While most major carriers seem to deal with rebooking, there is no OW guarantee as there is with IATA tariffs, e.g., that the late-delivering carrier is responsible for rebooking, nor does the EC 261/2004 "duty of care" scheme come into play, whereby the passenger's needs on the ground are handled during the flight interruption.

The baggage issue is a mess for tight connections and those involving a border, particularly for individuals who may have complex document issues, let alone prohibitive document issues. The connection issue will likely be dealt with through improved offerings from private insurers willing to step into the breach for a fee.