If I understand right, GBIF is one such platform. One disadvantage I find is doubling of data (Eg - submitting to both obs and eBird)Would be a dream if big platforms like these would share their database and knowledge; offering an option to upload observations to both to create one worldwide knowledge database. To ex/import the data between them is not very easy. Now it's a bit divided US/EU again.
Well, one can dream. I understand it's not easily feasible.