I would say yes too early - certainly in the high Alps (Upper Inn, Upper-Rhone, Upper-Rhine) early April is just too early. In the Ticino area you should be able to paddle, also in the Jura. When the melt starts-up it is going to be mighty as many areas have record snow. You would certainly find water to paddle but probably not a lot of the best stuff. In April a lot of Swiss paddlers migrate south - to Corsica, S. France, Slovenia, Greece etc.
May-June is probably a safer bet but it really depends what you want to do - rainfall/snowmelt creeking or the glacier-fed classics.
Having said all that maybe the unpredictable weather will prove me wrong this year!