The new ECS in SharePoint 2013 is pretty awesome, the Extel team has worked hard to make ECS on par with Excel. But wait what do these changes have in common with MOLAP? Well since most of the underlying Excel code is shared, a lot. Let me show you.
I created this Pivot table in Excel 2013 that points to the Adventureworks Molap cube. Nothing new yet here:
Now lets share this to SharePoint 2013, again nothing new here just a new UI:
Now lets open it in the browser, this is where things get interesting! Observe it looks very much like Excel 2013, and it even has a Pivot table fields list.
You now can change the pivot tables on the server (of course when you have the credentials) and add measures and rows and column all within the browser.
This is awesome! We now have a web based MOLAP browser that allows ad-hoc analytics. Just to make sure this is clear, this of course also works for Tabular 
.
Is the writeback functionality supported in browser?
Some of the new features in Sharepoint 2013 are inspiring, thanks for sharing your opinion about ECS.
I check this blog, because open it in the browser, this send me an error message about update in external data source and is impossible change the pivot tables, If I open in Excel then not problem present