If companies want to give employees an extra holiday then sure, go ahead. But that won't increase voter participation.
In general terms postal voting, and any method for voter-not-present polling, is open to coercion and intimidation.
That's why voting-in-person in booths remains the primary method, even in countries such as the UK where voting papers are logged against the identity of the voter ( it takes a court order to de-seal that information ).
In terms of invalidated votes, in-person seems to have about 1% of ballot rejections, whereas vote-by-mail has about 2% rejections. (No data on how many of those rejections were inappropriate and how many were appropriate that I could find). Citation: http://www.nytimes.com/2012/10/07/us/politics/as-more-vote-b...
In any case, I really don't see why this is such an important cause to prioritize:
1) Are there really good policies that are being held up by the voters that don't vote because of the inconvenience?
2) How does that compare with other uses of political capital (alternatives to FPTP, transit, anti-NIMBY policies, tax shifts, etc)?
3) What is the impact of low turnout vs electoral shenanigans in miscounting? Why not focus on having a more auditable system?
This article starts from the premise of "the most important thing to do is increase turnout, regardless of the costs [like those associated with a new holiday], and regardless of whether that improves policy". Sorry, I don't share that premise, and neither should anyone else.