Very very low. In terms of its route network to the UK, Eurostar has, since Brexit, been cutting it back rather than expanding it. This is because there is currently simply not enough capacity at St Pancras station for the new border checks, and they are having to leave some of their trains partially empty as there is no way to get all the people through passport control in time. This situation is expected to get worse before it gets better, as EES, the new Entry/Exit System for Schengen (which is to be introduced coinciding with ETIAS), will require collection of fingerprints, which the EU does not currently have on file for UK citizens.
As a result of all this, Eurostar have abandoned the two Kent stations and Calais, along with routes to the South of France, Disneyland, and the Alps. In addition, due to a situation beyond their control they are highly likely to have to temporarily abandon their route to Amsterdam as well. Until this situation at St Pancras can be resolved, the chances of Eurostar expanding its route network are slim.
However, in one very technically correct sense, Eurostar actually are expanding to Germany. This is because they have recently merged with Thalys, a company which runs international high-speed trains within Western Europe. Thalys will soon (from October) be rebranded Eurostar. You can expect to then be able to purchase through tickets from London to Germany, but it will still require a physical change of trains. Given the existence of Railteam (an agreement between high speed rail operators in Western Europe) guaranteeing onward connections with their "HOTNAT" (Hop On The Next Available Train) system in the case of delays by other operators, this through ticketing isn't actually as important as you might first expect. But you can perhaps expect a discount over the current cost of buying two tickets separately.