I think a middle ground would be the best approach. Don't stat up deities, but offer ideas and suggestions to help DMs stat up their own versions. This is for several reasons.
First, it gives the DM the freedom to decide whether mortals are capable of directly threatening deities at all. God slaying might be unsuitable for some campaigns. Even if a DM decides that gods can be killed, it should be up to the DM how powerful (what level) they are. Some DMs might like the idea that 10th level characters can challenge a god, while others might prefer for it be unfeasible before level 30 (or whatever).
Secondly, beings at that level of power ought to be at least a little mysterious. They're not like dragons, in that every high-level adventurer probably has a dragon slaying story. If the stats are in a book somewhere, some players will read them, and at that point they become less deities and more high level monsters.
Lastly, fighting deities should always be a challenge. This plays a bit into my second point. If the players know a god's stats, they can be much better prepared. Even if they don't mean to metagame, they might. For example, they might opt against getting armor that protects against lightening if they know that Thor ignores lightening resistance, which they might not have done if they hadn't known his stats. If the DM home brews the stats, the players never really know what to expect. They can attempt research, but they're limited to what the DM is willing to share, rather than what they can find in the Monster Manual (or Deities and Demigods).
Moreover, a stat block in a book is not designed with your particular party in mind. Even an incredibly dangerous foe can be potentially nullified with the right combo. As such, deity stats should be unique to the campaign (and therefore the party). No designer will ever know a DM's party as well as that DM, himself. As such, it should be up to the DM to put together such a challenging foe. I don't think that a DM should constantly have to custom-design every encounter for his party, but I do think that deities are a special case and deserve the extra attention.
With all that said, I think it's likelier than not that we'll see stats for deities. That's been the case in every edition thus far. Nonetheless, I think it would be counterproductive giving stats to every deity. Let's face it, very few groups are ever going to fight Thor, Ao, or The Lady of Pain. It's a waste of pages for most people. As such, I hope they keep the deity stat blocks to a minimum, and focus on excellent descriptions of those beings and good advice for creating the stat blocks yourself.