There is most certainly a future for existing vented systems, mine was installed over 42 years ago and I still have have my original (3) upstairs rads. The key factor in both systems is to avoid/detect any leakage(s). My system is still in pristine condition even though I have only added the odd drop of inhibitor over the years.
I have a bit of a bee in my bonnet re the recommended E.vessel pre charge and filling pressures as some boiler manufacturers were and still might be recommending that the pre charge and filling pressures are the same, if so, then there is no water reserve whatsoever in the E.vessel with a cold boiler which results in more (nuisance) frequent top ups but in lots of cases the top up PRV is left open all the time ("auto fill" mode) so one doesn't know of any leakage(s). Of course the same can be said of vented systems with a mains (ballcock) supplied F&E tank, I have a isolating (service) valve on mine which is "permanently" closed and I open it a few times per year to check for any make up/leaks, strangely enough I have never seen it making up even though one would think that there should be some slight evaporation from the open topped F&E tank.
I have also seen mentioned (on here) that some boiler manufacturers will not honour their warranties if the E.vessel is found to be of insufficient capacity which I find rather strange to say the least as a E.vessel is not a safety device, per se, since it can and does fail (ruptured diaphragm), the boiler PRV IS the safety device and is or should be always set to the working pressure of the boiler which in some cases now is 2.5 bar, it was formerly, in most cases, 3.0 bar.
A bit off topic but a plumbing friend of mine told me that he found it much easier to remove the baffles from a grant oil condensing boiler if he reduced the system pressure to 0 bar.