As I've mentioned above, it won't be long before seasons are ITSO only, and it'd probably not be too hard to issue outboundary day Travelcards on ITSO only too. Merseyrail Saveaways are mostly issued on ITSO now, to use another example of that kind of ticket.
I've been reading this thread for a while now what is a ITSO ticket.
Also I don't believe that Bletchleyite has got the correct ticket name for the Merseyside ticket he is thinking of, I think it's the Merseyrail Daysaver that is only valid on Merseyrail. The Saverway is valid on most ToCs out of LIV, buses and the ferry's.