Tip of the hat to Lamartine for the name.
Other mods have already proposed to extend the timeframe. This will, however, be as far as possible in keeping with the vanilla game, taking the 1836 POP and political setup and its economy as a baseline, and making only essential additions to, for example, the tech tree.
Tempting as it is to correct what many see as deficiencies, like the incorporation of Norway into Sweden and the absence of a separate tag for the East India Company, that brings the danger of 'mission creep' and will be avoided.
Because we don't know nearly enough about the game yet, we are more or less restricted to internal politics, leadership and the general political setup, assuming Clio was adopted without modification for those areas we have not yet been shown as screenshots.
I'm almost certain to be indisposed for at least a month after the release date so will have little or no time to do the spade work. This thread is purely for sharing research and discussion.
The start date would be the [EDIT] Second Treaty of Paris - 20th November 1815 - with a few little problems left to straighten out in Europe and Latin America in a state of chaos. Serbia too is fighting its independence war.
The twenty extra years would take in a Spanish civil war, the independence of every Latin American state, Texas, Greece and the Romanians, the high noon of reaction in Europe, the beginnings of the Industrial Revolution, the consolidation of Company rule in India, the rise of Mohammed Ali and the destruction of the remnants of Polish independence.