Didn't they already announce that they were specifically NOT going to indicate it?
If that's true, they're completely insane. Surely they realise that anyone running a real Reno Jackson deck is going to be tracking their deck anyway? Either with a tracker or just with pen and paper. I mean seriously.
Liquidhearth's Wing One preview states it, but no source provided: http://www.liquidhearth.com/forum/hearthstone/498238-league-of-explorers-card-review-wing-one
Pretty sure the source here is Ben Brode's response to a question about Reno at Blizzcon. The question was something like "Hey Ben, so this new card Reno Jackson heals your hero if there is no more than 1 copy of each card in your deck. I was wondering if there will be a feature like Hearthstone tracker to help us with it?" and his response was something like, "Well, we're definitely not going to do an entire tracker. We might talk with development about what some of our options are for a more simple supplement that helps with cards like Reno. But there definitely isn't anything like that being released as League of Explorers comes out."
I think it's a misinterpretation to assume there will be no yellow outline based on this response, since Ben Brode might have been strictly answering the question, will we get a full tracker/ will we get a similar complex feature like little dots on Reno in your hand, one dot for each duplicate card still clogging up your deck. The binary simplistic yellow or not is not what the question was about, so much, it was using the increasing complexity of the card design to try to petition for some more tracking features really. There might be a yellow outline and Ben Brode doesn't even know about it.
Blizz definitely isn't making a conscious design choice to withhold yellow outline. If they forgot it, or are putting it off because the coding is more complicated than Tinkertown Technician, people will whine and we will surely get it, really.
Even with the yellow outline, a tracker is a little more useful if you aren't good at tracking your deck on your own. If there's only 1 dupe left in your deck, hold onto reno and try to heal, if there are 2 dupes left in your deck, fuhgeddaboutit better start hammering their shredders with Spectral Smith to try to stay alive.