Can't do it, that would almost certainly violate the paypal TOS, and even if it didn't it would probably violate money laundering laws. We can't help people go from usd to crypto. There are too many very-high-barrier regulations.
Down the line though, we should be legally able to help people go btc<->siacoin. Some hosts/nodes will have both btc and siacoin and will serve as market makers, you can then use payment channels to trade with them. That's a long way down the line.
Like any major new technology, there are going to be barriers to entry and it's going to take time to bridge them. It's something that's heavily on our minds, but it doesn't matter how easy it is to get siacoins if the storage platform isn't very useful (if say, you're limited to 500mb files and can only upload 1 file at a time). So our biggest focus is making something that people will want to use. If it's worth the pain of getting siacoins, then that says great things about the platform and its future. The barriers to crypto are slowly being removed (Coinbase just announced an instant exchange platform, for example), and everyone benefits from that.
We'll be doing our part in the coming months, but our immediate goal is to make the storage platform better. Without a worthwhile storage platform, we're just another altcoin.
+1. For now BTC is the bridge to Siacoins. With this bridge, everyone in the world can use Sia platform and Sia saves the hassles to deal all kind of different fiats in the world. In the long run, Siacoins will be in all major exchanges and it will not be a problem for people to trade Siacoins if Sia as a platform works well.