I have practiced often at Iwama-Ryu dojos and they teach Ikkyo started with a Shomen-Uchi by Nage not Uke. Of course Iwama claim that they teach the original style of Osensei. Whether it is true or not is not for me to decide, but if it is true, then Osensei taught attacking the opponent first. If I remember well, I've read somewhere a quote from Osensei saying that you will feel with your Ki the imminent attack of your adversary and then you should provoke and lead the attack by striking/entering first. Thus you control the situation not the opposite.
On the practical side, I've noticed that for a not so proficient Aikidoka such as myself, waiting for the attack to come might be too late for me to react. In my pre-class bullying of my Aikido pals, I noticed that fainting an uncommitted Shomen-Uchi to my partner will automatically cause an instinctive protective response which is an excellent opportunity for an Ikkyo. It has never failed me sofar, even when my partner knows what I'm doing.