Most professional traders/investors believe that the much anticipated altcoins season will not commence except there are reasonable melt down of the dominance index rates. As a matters of facts, Bitcoin dominance index rate is still bullish at 63% as at the time of writing.
The fact that bitcoin dominance index rate as you said is still bullish means we are still far away from seeing altcoin.
The bitcoin dominance can also do sideways and it'd take quite a while before it will go down.
There's also possibility that it won't go down at all, the total2 chart looks pretty bearish in my opinion.