While it's a good election result for Sinn Fein, it doesn't bring a border poll success any closer. The problem is that there is a much greater chance of a successful border poll if it isn't led by Sinn Fein. The numbers breakdown is approx 40-20-40 and the middle ground is where it will be won and lost. That together with the 33% of current non voters. Unionist politicians have done almost everything in their power to alienate the 20% middle ground with their decisions in recent years but there is still a lot of ground work to be done to convince a sufficient amount of these same Alliance voters to vote to change the status quo. This will be won and lost mostly on economics, health, education and the day to day stuff that matter to people. Therefore it is more important that SDLP or other shades of civic nationalism gets behind the preparatory work. Sinn Fein support for a UI is a given in the same way that DUP/TUV is a given on the unionist side.
The key to moving forward is as you rightly say , 'the preparatoty work' . What will a UI look like, its implications for our unionist neighbours, how will their identity be perserved , will there be a NI assembly , leading to full integration down the line.
Unlike Brexit, these points all need addressed thought through and agreed , so no one is left in an uncertain future.
All parties need to look forward to discussing at all level of the politic.