Teija Tiilikainen, the State Secretary at the Ministry of Foreign Affairs and one of the leading EU policy thinkers in the country, wrote a column (fi) on the EU in Turun Sanomat. The Finnish News Agency (STT) summarizes:
"It is not possible to take that many further steps from the current level of off-step without causing the EU as it stands today to disassemble and a wholly new system to arise," Ms Tiilikainen writes.
"Yet there has been no serious debate between member states over this radical change."
Ms Tiilikainen added that certain member states or groups of countries could continue to be allowed to proceed faster or slower in integration, but only on the condition that the bloc's "common decision-making and norm system" was not damaged.
"If however one is referring to a situation where the EU's current institutional makeup would crumble, in the name of realism one ought to sketch out the appearance of Europe after the tumult."
As examples of the current multi-speed system - presumably tolerable ones - Tiilikainen mentions the EMU, Schengen, and opt-outs for individual countries.
I'll note that Finland has opposed all sorts of multi-speed arrangements inside the EU and the government's thinking on the issue may be pretty close to the column. The argument of course cuts both ways: against laggards who want more opt-outs and against enthusiasts who'd like a nucleus to hurtle along the route to federalist nirvana.