Talking about it? Maybe … could you jog my memory when he did that?
But I’m doubtful about the working toward it. Book- and show-Varys have worked toward a restoration of Targaryen rule. They were not known for their inclination to accept limits set by non-Targaryens.
And even though Daenerys has shown a remarkable disposition to listen to advisers, they are just that - chosen by her, heard by her, at her will ignored and dismissed.
If Varys had that much interest in a constitutional monarchy, he chose an odd champion [and Viserys would have been worse].
Wouldn’t Varys’ interests have been better served if he had steered the government of the Seven, well, Six Kingdoms toward more influence for the Council, the major Houses and the most important centers of commerce?
Due to Robert’s disinterest in politics, power had already spread around. The impending monetary crisis, caused by Robert’s overspending, would have given the Houses a wedge to insert themselves into such government processes - they could have formed a Westerosi version of the Magnum Concilium with some legislative powers over taxation and spending, for example.
From there, it’s still some way to go before a House of Lords is established and a longer one before you constitute a House of Commons, but it would have been a much better start to reform the government toward a constitution than ignite a full-blown war to make Westeros too weak and too dispirited to withstand conquest by a foreign army of savages.
I have never understood, why Varys’ actions have been met with so much sympathy. Sure, it was Littlefinger who fired the starting pistol for the war, but if he hadn’t been around, Varys would have had to do something similar eventually - and, as we know, the conspirators had their own plans to that effect … Littlefinger just got there first, before they were ready.
And while Littlefinger’s motivation might look worse than Varys’ - as it was totally self-centered - was it really?
Take a look at the Targaryens! They had no qualms to use WMDs to conquer and subdue. They followed an ideology that put them above all other (lesser) beings, and their customs made sure that they continued to be an alien presence on the continent they ruled and within the society they shaped*.
Their demise was inevitable once they ran out of those WMDs, and social inertia was slowly overcome by the demands of their rule on their subjects.
And Varys should be clever enough to know that a rule by a much diminished Targaryen presence could only be temporary, before another civil war is going to envelop Westeros once again.
- Which doesn’t mean that every single Targaryen saw it that way, of course. But the ones in power, and the ones craving for it, can often be associated with a belief in their own superiority … not surprisingly.