It really depends on the sellers financial situation. Most sellers in this market are selling because they have to and need the proceeds from the sale now rather than a year or 2 from now. However, it doesn't hurt to ask. Keep in mind that if the seller does consider a lease to own agreement they still will want to know why you are looking to wait to close, how much of a down payment you currently have for the future closing of their house and what your credit score looks like. If you are delaying a purchase due to a credit or financial situtation speak to a mortgage lender ahead of time to find out what you will need to do to get approved for a loan down the road and get something in writing that shows you are a good candidate or will be to buy their house. Good luck
The major drawback to a lease to purchase option would be the loss of the downpayment if you do not meet all the terms of the agreement, and if you are unable to secure financing to be able to purchase the home. In addition, if the neighborhood is not right for you or if the market takes another downturn, you might find yourself questioning why you entered into such an arrangement.
That being said, most home owners looking to sell their homes today are not interested in this type of arrangement. In many cases, they need the cash from the equity in their home to purchase another home or for other purposes.
Your best option is probably continue renting until you find the right home that best meets your needs.