Alright, I misunderstood and assumed that Napoleon III was an actual absolute monarch. So focusing on the second half of my question, is ttl's France inevitable going to lean into conservatism or would the left and right factions be more even (with future events shaping public opinion of course)?
Eh, not a true expert on late 19th Century France, but IMO it would still end up seeing a stronger left and more democracy (though not as much/fast as OTL's 3rd Republic). After a well-deserved and self-evident victory* against Prussia and its German allies, NIII will likely have gathered enough moral authority and influence to (mostly) keep the factual reins of power until his death, even if he manages to live a decade or two longer than OTL.
His heir however, will have to deal with the inevitable rise of socialism (essentially tied to industrialisation). Combined with the rising literacy rate, the people will be starting to demand more
factual democracy, rather than mostly
theoretical democracy. The already existing universal vote will mean that French socialists will get more legislators at a faster rate than their peers in the UK, Belgium or Prussia (with its
Three-Class voting system, not to be confused with the OTL German Empire's Reichstag, which
did have universal male voting).
That being said, there is still quite some leeway with this: the OTL German Empire did not witness any majority coalitions in the Reichstag taking over the factual reins of the Empire from the Imperial government (though it very well might have started happening during the twenties or when Wilhem III would have taken the throne if not for WWI), while Belgian kings went from actual leaders having to play parliament to get their way (Leopold I & II, less so Albert I who still actually commanded the army in WWI, Leopold III getting into trouble for staying on that path for too long, though
surrendering the army didn't exactly help his position), to a kind of moderating advisors you can't blatantly ignore, to de facto figureheads (this one admittedly after WWII) without seeing their constitutional power change one single bit between 1831 & 2021 .
A major difference between Belgian Kings on one hand and German & French Emperors on the other, is that the former needed to have all his actions countersigned by a minister, while the latter two didn't. That does make it easier for political parties to take over the real power, but it is not an absolute requirement.
In any case, I do foresee either more actual constitutional reforms by 1900 (or even earlier), or implicit ones, like the Corps Législatif subtly making clear to NIV that they will block his governments bills & budgets if he does not appoint at least some of their preferences as ministers. More labour rights are also a given, even Imperial Germany went down that road (to defang the socialists).
Constitutional doesn't mean just having a constitution, especially so in the context of France.
As per article XVI of the Declaration of the Rights of Manand of the citizen:
"Article XVI – Any society in which the guarantee of rights is not assured, nor the separation of powers determined, has no Constitution. "
So with Napoleon III having most of the legislative power in 1852, there is no separation of powers. After 1869 yes, the second Empire could be defined as a constitutionnal monarchy.
Interestingly, the Imperial Constitution of 1852 (which is technically just the amended Repubican Constitution from earlier in the year) actually starts with a reference to that.
Article 1. - La Constitution reconnaît, confirme et garantit les grands principes proclamés en 1789, et qui sont la base du droit public des Français.
"The constitution recognizes, confirms and guarantees the grand principles declared in 1789, and which form the basis of the public law of the French."
This nicely shows how there can be major differences between the official state of things on paper and in theory versus the actual reality.
I believed that the plebiscite was due to trying to save face after losing Alsace-Lorraine. Was this correct or was there pressure building to democratize before that?
All imperial plebiscites happened
before the war, the last one in
April 1870, the Emser Depeche which triggered war happened in
July.
The April 1870 change was mostly to consolidate the 11 amendments to the (initially) republican constitution of 1852 which technically was still in force. From a quick read, it also appears to reaffirm and reinforce the sharing of powers between the emperor and the legislature, while also curtailing the power of the (fully appointed by the emperor) Sénat. Now, as mentioned above, the glory of winning a major war would likely help NIII limit the actual result of his power weakening on paper, but his heir won't have the same advantage.
* In the minds of French public opinion, which doesn't know a thing about the merits of breach-loading artillery or the elder Moltke's organisational & planning talent; but which does very much remember France being Europe's preeminent military power since centuries.