The law is about "harmonisation of charging protocols" and currently USB C is just the standard for everything, so it is set as the target for people to "harmonise" to. They don't specifically require the standard to be USB C and if a new tech comes out that is clearly superior, the law mentioned a Commission can be formed to make a judgement on switching.

Page 17 of the law document.

> The Commission shall continuously assess market developments, market fragmentation and technical progress with the view to identify categories or classes of radio equipment capable of being recharged via wired charging for which the inclusion in Part I of Annex Ia would lead to significant consumer convenience and reduction of environmental waste. The Commission shall report such assessment to the European Parliament and to the Council, for the first time by [3 years after the date of entry-into-force of this Directive] and every 5 years thereafter, and adopt delegated acts pursuant to Article 3, paragraph 4, first subparagraph, point a) accordingly