Ynet has a two-part article (the more important half here) detailing a unique solution to the problems with the observance of Shemittah in modern day Israel.
Now while the author, David Golinkin, is a Conservative, his thesis still deserves attention. Basically he brings three concepts of modern day Shemittah to the discussion. The first is that it is still D'oraisa, something most Poskim reject. Shemittah hasn't been that since the destruction of the First Temple. The second is the consensus of most rabbonim for over 2000 years which is that since the first destruction, Shemittah has been a rabbinic mitzvah. What is interesting is that he has found evidence of a third concept, that Shemittah is Midas Chasidus, in other words, completely optional in today's society.
If true, that would solve a great deal of problems. A farmer wishing to observe Midas Chasidus could observe Shemittah either strictly (the Chareidi approach) or through Heter Mechirah (the approach of some of the Dati Leumi). One who didn't wish to could simply claim he's not a chasid. There is no obligation, after all, to observe Midas Chasidus.
The problems with Prof. Golinkin's thesis are:
(a) Rav Kook and the Chazon Ish, generally seen as the original leaders of the Heter Mechirah vs No Heter Mechirah debate, were surely as aware of the Midas Chasidus option as he is. After all, the poskim that Golinkin lists, such as the Rashbam, the Rashbash and Rabbeinu Nissim, were hardly unknown sages. If the Chazon Ish did not mention Midas Chasidus as an option, certainly it was because he did not feel it was a viable choice. As for the Heter Mechirah side, I have only rarely seen Midas Chasidus used as the reason to observe the Heter and then it is invoked to convince people to accept all the leniencies needed to make it work in the face of all the objections.
(b) The statement of purpose that Prof. Golinkin notes is also incorrect. Firstly, while it is true that the secular Zionists did not build Israel just so they could either give it or sell it to the Arabs once in seven years, they also did not build it so that Shemittah, or any real Judaism would be observed there. Remember that the purpose of secular Zionism from Herzl to Ben-Gurion was to build a non-religious state so Jews could prove that they could be a people "like all others". As for the religious Zionists, the purpose of building Israel was to fulfill God's wish that the beginnings of the final redemption commence. Along with the responsibility of living in and tilling the ground of Israel came the obligation of Shemittah. Heter Mechirah was a controversial solution to a big problem.
(c) Even if a large number of prominent rabbonim supported the concept of Midas Chasidus as the modern reason for observing Shemittah, the rabbinic leadership since that time has overwhelmingly supported the idea that Shemittah nowadays is a Mitzvas D'rabbonon. It is a usual tactic of the Conservatives to dig up rejected, forgotten or minority opinions that fit their mode of thinking and declare that these are all viable halachic options. Unfortunately, that's not how the system works.
(d) Prof. Golinkin's final point illustrates the usual flaw in Conservative thinking, that since times have changes, the solutions in halachah must change with them:
In the final analysis, what is the purpose of Shmita? “That the poor of thy people may eat" (Exodus 23:2). Today, almost no one fulfills the commandment's purpose as it appears in the Torah. Therefore, it would be most appropriate for all Jewish farmers in Israel to donate a percentage or a fixed amount of the Shmita year's profits to poor people. In this way, the original purpose of Shmita will be achieved.
In the final analysis, we observe Shemittah not because of feeding the poor or letting the land rest so it can regain its fertility. We observe Shemittah because God told us that once in seven years we were to let the land lie fallow, like it or not. Yes, the poor do not go and glean the fields like they did 3000 years ago but that does not change the essential obligation of Shemittah. We do not say that just because the poor don't go and take their sustenance from the fields that we can't observe Shemittah. In Conservatism this might be logical but not in halachah.
Despite these criticisms, the article does bring an interesting idea to the table, one probably worthy of further discussion in more learned circles.