Well, building HST would be a way to make way for freight. At any rate, the Swiss do such planning in the integrated way. E.g., say the proposals for enhancements in the Basel area include a bypass route for freight to have more capacity for new TGV-Est, DB Rhine valley route related high-speed traffic, plus extensions for the local rapid trains.

Switzerland's geography doesn't make an expansive highway system feasible.

Still a referendum was needed to stop their expansion, and voting down both proposals in another referendum to prevent the lifting of that prohibition.

So far, I see the big problem as scheduling.

(1) Infrastructure Branch builds a new line with 1.5 kV DC and both ERTMS Lev 2 and old signalling system, Operator Branch runs some local and some international trains with dirrerent locos; (2) Infrastructure Branch builds a new line with ERTMS Lev 2 and 50 Hz / 25 kV, Operator purchases two-system locos with both signalling systems for all trains. In this case, which version is cheaper (a) for Infrastructure Branch, (b) for Operator, (c) for the entire railway?

Similar examples could be made about each of the issues I (and you) brought up downthread in connection with the question of international compatibility, e.g. infrastructure investment planning influences vehicle and operation planning and vice versa, also in cost.

A lower maintenance threshold for rail vehicles will result in higher track wear, and vice versa. This is (unfortunately) visible most strongly in my region, but also appears more to the West. Compare French and German high-speed tracks and operation, in particular rail polishing train operation and night freight trains. Or, again, pre-Hatfield British policy.

There would no longer be just "railways" but "passenger rail" and "rail freight".

This can bear strange fruits like the abandonment of the idea of universal locomotive just when it was made possible by technology (and reality in Austria [and France and Switzerland until recently]), or the separation of maintenance shops which results in longer routes to repair; e.g. cost increases where capacities are doubled and operational problems where they can't.

With less power but more freedom, it might decide to restart the express freight business which La Poste abandoned

The problem is that at present, railfreight is the most losing branch for railways. That is, on its own, it is least able to bring up capital, while integrated, it is at least possible (even if in reality rarely prioritized) to branch off money from profitable high-speed (or subsidized local passenger...) services. On your example, I tink a cross-railway offer involving utilisation of the high-speed lines with new or rebuilt-from-express-passenger-cars and series 36000 locos would

Regarding the issue of what is needed infrastructure-wise to separate passenger and freight, or at least to give freight a stronger background, I can think of two things.

The first is a strategy to separate freight and express passenger lines along the same corridors, be it by adding extra tracks, building high-speed lines and/or freight bypasses, or using close-by parallel lines intelligently; paired with fitting the lines intended for freight with tracks for high axleloads. This part is actual EU policy.

The other part is not EU policy, and pursued by only a few governments (and even them lacklustre): to maintain a network with a high number of access points, to subsidize local wagon or sub-wagon-load freight and industry access tracks. To count on customers opting for re-loading from local trucks proved a folly too often.

_{*Lunatic*, n.
One whose delusions are out of fashion.}