Grammar Pedantry Warning!!
"You take" is not "present" tense, but, rather present simple and is used for actions that are repeated over time. "If you take" is conditional tense and typically follows that the conditions must be met before the second part of the sentence occurs.
Such as, "If it rains, I will take an umbrella" would be most common. If/can clauses are also typically read this way. "If I have a driver's license, I can legally drive a car" would be a good example. Without the conditional, the result is not possible.
So, a grammatical reading of "If you take the Attack action on your turn, you can use a bonus action to try to shove a creature within 5 feet of you with your shield." would read that the Attack action must be taken before you can take your bonus action. The Attack action cannot be broken up - additional attacks are not additional actions. They are simply part of the same action.
(Barring, of course, specific exceptions like moving)
The RAW reading of this, coupled with an actual grammatical reading would support Crawford's interpretation. Conditionals are not read as suggestions nor are they read as having more conditions than what is stated. If/then conditionals are what they are. You take the Attack Action, then you can take the bonus action from Shield Master because the condition for taking the bonus action is that you take the Attack Action.
Now, granted, I won't be changing how we do it in our game. But, from a RAW reading, yes, I can see why this would be the RAW interpretation. For you to take the bonus action in the middle of the Attack Action requires reinterpreting the Attack Action to mean that gaining multiple attacks creates multiple Attack Actions, which can be interrupted. However, RAW doesn't support this. Attack actions are discrete - regardless of how many attacks you actually make.