Do you have any evidence to suggest the 717s will be better than the 700 or just hope? At least the single 313 can go out alone with no real issues. The only reason the 313s are getting worse is quiet rightly no-one is spending money on them.
Neither evidence (none available yet) nor hope (not a line I use often) but reasonable expectation. No manufacturer of high-value products fails to learn from in-service experience of new product to improve future production. Especially true when said manufacturer has ongoing responsibility for maintenance.
I wouldn't say there is much evidence of the 313s getting worse. They may be cutting back on the cosmetic stuff, but they seem to be holding up mechanically pretty well, just what you'd want to see for a unit nearing end of service.
A failed train is a failed train no matter how long it it, it blocks the line.
Agree - but the a train consist of two units will fail twice as often as a single unit of the same type. Statistically speaking. Hence the MTINs of short units need to be much better than longer units, to get similar train performance.
The 700 we were told would never fail before they were introduced, so forgive me if I am not expecting any improvement on reliability before 2020.
Never fail is just an impossibility, for pretty much anything, anywhere. Even promising good availability for a completely new model type is indicative of a lack of experience, at best. The well-known bathtub reliability curve is widely applicable, as any component can suffer a manufacturing defect which shows up early in service (the unfortunately named "infant mortality" issue.) The underframe case explosion on the retractioned 455s are a great example of this - a component which is normally so reliable that no mitigation for failure was considered, unfortunately had a human-error defect introduced in manufacture.
My take is the 700s are now in the same reliability range as what they have replaced,when looked at on a train rather than unit basis. They will likely improve further.
One thing that really concerns me is the turn around times on the 717s. Will they be walk to other end and go like the 313s are or will we need to wait for computers to reboot. If it is the later considering in the peak may trains inbounds are delaying the outbound things will get much worse.
No knowledge on this, but you would expect that the turn-around requirement was written into the train specification. One saving grace is that software enhancements are much easier to deploy post-introduction than hardware or electrical issues, so if it's not right on day one, a fix should be deliverable without too much disruption.