I am getting close to the first fix of renovating my house and wanted
to test out an idea I have been thinking about on the plumbing side of
things.

These are the two main unchangeable factors I have already decided upon

1) I am going to have a new decent combi condensing boiler
2) I will be having 2 showers. One in the main bathroom and the other
in an en suite.

So the obvious problem is that when both showers are in use at the same
time one will suffer for sure.

First Solution - Replace one thermostatic shower with an electric
shower. But more costly at say 3/4 times more per electric shower use.

Second Solution - Have thermostatic shower and an electric shower side
by side and use whichever is dictated by if the other is in use. Kind
of weird looking I imagine.

OR Supply warmed water via a mixer valve to the electric shower.

The advantage I see here is if there are no other demands on the hot
water the electric shower will be supplied by warm water (set at max
safe temp) so the electric show would only have to rise the temperature
by a small amount. But if hot water is being used elsewhere then the
electric shower will then pretty much take over heating the water..

This idea seems to worki n theory in my mind, but my knowledge of
practical plumbing is limited (this will have change as I'm going have
a go doing all the plumbing myself). One problem maybe is that I have
assumed a method/device exists that allows you to prioritise supply of
hot water to different places.

Another factor that might help me out is that I have very high mains
cold water pressure (my cheap hose pipes expand to twice there width!)
and something close to 50 liters a minute flow rate.