the thing is, the effects and timescale of hormones varies based on genetics and what seems like luck. some trans women find after a few weeks on HRT they totally stop reacting down there, others have been on hormones for decades and still rise to the occasion when needed.
I think most find that though random activity bellow the belt is rare after a few months, most can still get most of what they used to have when they need it. though it may take more work to get there and it may not sustain itself as well as it used to.
Dependent on how your wife deals with your transision and where her sexuality falls in this situation intimate activity can continue all through your transision though it may evolve over time to include more manual, oral and toy based activites and your sex lives may in time more resemble that of two women than a hetero married couple, which is really whats happening.
Also don't give up hope or sell your wife short before things have happened, if she considers herself straight and would never have considered sex with a woman before, that dose not compleatly rule out that her love for you may lead to her exploring where exactly the boarders of her sexuality stand.
I think the best advice I can give for you and your wife is to take things slow, don't try and force each other into anything, talk and listen to how the other feels and try and figure out what you each need, and if you reach a impasse don't let it frustrate you, just try and find the most agreeable solution. then again that is also the best advice I can come up with for any couple so nothing really changes.
Serena