Is this for the next version? Or are you saying it can work now?
As far as I can tell, if the two Macros are currently named:
K
Keynote
I get this (where I can hit return to choose my Keyboard Maestro macro)

I like this single letter method and currently use it to denote which Macros should be my "default" Macros in the Conflict Palettes. In most cases I know what the single letter stands for (by including an Icon that makes sense). But I would prefer to be able to name my "default" Macro by more than a single letter and still have Return select it from the Conflict Palette.
If they are named
Keyboard Maestro
Keynote
I get this (where b and n become the deciding characters)

If they are named
(space)Keyboard Maestro (i.e. with a blank space in front as @hello suggested)
Keynote
I get this (where the Spacebar triggers my Keyboard Maestro macro - which is very good and in fact actually better than my Single Letter naming system as the Spacebar is easy to hit and I can give the Macro a full name rather than using a single letter. So, a big thank you to @hello for that.
To make any Macro the "default" in the Conflict Palette I simply add a space in front of its name.

But if they are named
Keyboard Maestro
Keynote
I get this (i.e.
is not the deciding character)

But are you saying that in the next version, naming the first Macro
Keyboard Maestro would make
the deciding character? In other words, be able to set a Macro as the default to be triggered from the Conflict Palette?
Or are you saying there is a way of naming my two Macros to achieve this in the current version?
Thanks Peter! Sorry if I have misunderstood.