No, that is not possible. Just imagine that a given Marketo lead might be involved in 2 or more opportunities. In this case, what would the token render ?
But you could also create your own tokens for programs (Understanding My Tokens in a Program - Marketo Docs - Product Docs ). Amongst the program token type are email scripts, only for emails. See here for the velocity tokens : Email Scripting » Marketo Developers
Since you can't use opportunity fields as tokens as mentioned, one solution is to mirror that opp field on the contact record.
So have your CRM admin create a custom field on the contact object called Reservation End Date and a workflow or trigger that populates the custom contact field from the custom opp field. Then that custom contact field will come into Marketo and you use it as a standard token as you want.
Keep in mind though that if a contact has more than one opp they could also have multiple reservation dates.