I think that would be a great idea. I would actually prefer English voice actors though, but only if they hired decent voice actors and didn't make Link a loudmouth like in the cartoon series. I don't mind if he speaks, but keep his voice in line with his character. Give him a soft tone: never make him sound like's trying to force a situation, and keep screaming, and talking in general, for that matter, to a minimum.
However, if that is not an option, I would very much enjoy seeing a Zelda game with an actual Hylian language. I think, depending on where it is in the timeline, it should be a mixture of (extremely) garbled English and a completely new language. The earlier in the timeline, the closer to garbled English it should be, with more and more of the new language added in as time passes. They could even make the direction the language develops vary a bit in alternate timelines. Or, I wouldn't even mind if they just used Japanese. I mean, Zelda obviously is not meant to take place in this universe, so whatever language they use could be considered canon (for whatever particular region it is used in) in the Zelda multiverse.
To sum it up, I think this, or any good voice acting, is a great idea for the series.