My LOR was extremely resistant to the idea of a strictly online "no physical Kinyan" sale until last year.
We came up with a form (the only option last year, this year he allowed people to contact him to do a traditional Kinyan if desired) stating name, address(es), some other specific questions and then a "full name as signature" line, similar to the way that many legal forms are handled online - both government and business. Is it a perfect solution? No. But it matches, as I understand it, the normal way of handling secular business online. There are exceptions - e.g., a full banking relationship typically requires some signed/faxed/scanned/printed paperwork initially to start the process - but for most "small" transactions these days, this is really quite typical.
This is combined with, as I understand it, the Chametz sale - both appointing the agent and the process by the agent to the non-Jew (which I found out recently was also done last year without the usual Kinyan or a handshake (which is "secular way to finish a deal")) - is not a Halachic process per se, but rather a business deal. For me to appoint someone as a Shaliach for a Mitzvah is bit different (though conceptually similar) than for me to appoint someone as a legal agent for a business transaction. I think that is the key: Business transactions can be done in a number of different modes, which vary depending on the local (i.e., secular/government/general business) laws and customs.
That is different from, for example, the modes of transaction for a wedding or divorce, which are very strictly regulated based on thousands of years of Halachic rulings. You can't (I don't think...someone will probably prove me wrong!) replace a Halachic wedding or divorce with "click here", but you can replace a lot of other things - e.g., announcing a found object is not about the exact format of the announcement but about getting the word out, so sending to your local Jewish email list works as well as (often much better than!) announcing in Shul or in the marketplace.