What would the european parliament be like if it was appointed today ?

It would be very similar to the current parliament, no matter that the UK is gone.

The political landscape in a lot of european countries has changed pretty fast since the last european elections, for example in France, where En Marche ! Is now the first party or in Wallonia, where the latest poll suggest that the socialist party will loose a lot of its seats during the following elections. But, when you look at it, for the european union at large, not a lot of things have changed. The only important fact of this agregate of poll is that the GUE/NGL (european far left party) is clearly on the rise, when the ALDE is also. The conservatives of the ECR on the meantime suffer a lot from the uk's leaving of the EU, their first party where the Tories.

(the - and + are the difference since the last election in 2014)
The socialists in numerous european countries(e.g. France, Belgium, Netherlands) are falling but on the european scale, the socialist seems to be ok.
If the parliament would be elected today, the EPP would still be the leading groups and its candidate would still be the chief of european commission.
In the meantime, the greens are completely collapsing, it may be because in a lot of countries, they won in 2014 a seat on the razoredge, for example in Croatia.

If we look now the group that would be the first in each country, we can see that the ALDE would gain a lot of countries like France or Czech Republic. The GUE/NGL would loose their only country, Greece and the Movimento 5 stelle would be the first in Italy, that would mean EFDD is the first group of the country.

Technicals details :
I gave the seats of the UK using a pan european list of MEPs elected proportionnally in the whole EU. It isn't officially how it would be, but some european politicans such as Emmanuel Macron have endorsed this. I used latest polls from each country to know what would the votes be, it isn't a poll onto itself, it's an aggregate of poll. All details of how I've made this and all the figures are there. (it is wrote in French, sorry).
http://nullupload.com/download-af11c5061e (the sources, in French)
http://nullupload.com/download-59412b2fca (the spreadsheet with everything, in english)

The map of europe and the parliament pictures are under CC BY-SA 3.0 licence. They're coming from Wikipedia and have been modified to show the results I've calculated. The 2 graphs are under CC0 licence and the text is under CC BY-SA 3.0.